'97 Concours dash lights won't stay on

[human]

I've got an annoying problem with my '97 Deville Concours. The dash lights won't stay on. If I have the Twilight Sentinel turned on, they may or may not come on at all, depending upon whether it's totally pitch black outside or not. When the dash lights go off in this mode, the headlights revert to daytime running light mode. If the TS is turned off, the dash lights will come on if I turn the headlights on manually before I start the car. Although the headlights will stay on, it's a crap shoot how long I'll have dash lights. Maybe they'll stay on for the whole trip or maybe they'll go out 30 seconds after I start the car. It's very annoying. Once this malfunction occurs, the dash lights will not come back on for the duration of the trip, nor will the dome lights will come on when I park and open the door. The car must sit for a little while before things reset. If I park, get out, and then come back a minute or two later, the dome lights are still out when I open the door. I'm not sure what the minimum reset time is.

The only trouble codes I've pulled that seem remotely related to this problem are B1971 (Inadvertent Power) and B2471 (Int. Lamp Fault).

Any ideas of parts that might be bad? The ones I've considered are the Inadvertent Power Relay (Inadvertent power fuse is fine), the light sensor for the Twilight Sentinel (where is that located and what does it look like?), and the headlight switch cluster, which is a single unit containing the pull switch for the headlights, slider switch for the Twilight Sentinel, and buttons for the trunk release, fuel door release, and fog lamps. Fog lamps seem to be a very rare option for '94-'99 Devilles. There always seems to be a dozen or so of these switch clusters available on eBay, but I have yet to see one, new or used, with a fog lamp switch.

As you can imagine, this problem is very annoying and my cash flow is tight these days, so I can't afford to indiscriminately throw parts at the problem in hopes something will fix it. Any insights would be greatly appreciated.

[Cadillac Jim]

It sounds like a bulb somewhere is shorted, or is shorting occasionally. This can happen with a broken or burned out bulb. Since it seems to be intermittent, you can start by turning on the parking lights and walking around the car. Don't forget the small bulbs in the running lights on the sides of the fenders, and the small bulbs near the license plates. Look at the bulbs in the trunk and under the hood, too. There are also two bulbs in each sun visor.

[human]

I checked all the lights and everything is working except for the little red ones on the rear quarter panels. Are these lights or just reflectors? Also, the dome lights worked when I first the driver's door, but did not work while I was opening and closing doors as I checked the other lights.

It sounds like a bulb somewhere is shorted, or is shorting occasionally. This can happen with a broken or burned out bulb. Since it seems to be intermittent, you can start by turning on the parking lights and walking around the car. Don't forget the small bulbs in the running lights on the sides of the fenders, and the small bulbs near the license plates. Look at the bulbs in the trunk and under the hood, too. There are also two bulbs in each sun visor.

[Cadillac Jim]

I would have to check the FSM but my Eldorado does have bulbs in the rear quarter panels just in front of the bumpers. You can check by looking behind the sheet metal with a mirror for wires. Ask where you have your oil changed for them to check and replace any bulbs that are out and that should do it. If one of those dark bulbs is shorting, that should fix your problem.

I don't know the dome light logic on the Deville. On the Eldorado, the map lights serve as the courtesy lights and there is no dome light. If it quit happening for you, it may be related to your dash light problem. If replacing the running light bulbs doesn't do it, someone here (likely me) will haul out the FSM and look for something else that could cause intermittent dash lights in the schematics.

[human]

By "dome lights", I am referring to any lights that come on automatically when a door is opened. This would include: front and rear map/reading lights, marker lights in the door panels, and under-dash lights that illuminate the front floorboard area. These will come on whenever things are functioning normally, but when the malfunction occurs, none of them come on unless turned on manually by twisting the headlight pull switch or, in the case of the individual map/reading lights, pushing on them to manually activate them.

[human]

For some reason, I haven't been able to let go of the idea of the inadvertent power relay as the cuplrit, so I stopped by NAPA on my way home from work this afternoon and picked one up. I drove the car this evening with the twilight sentinel on and had dash lights for the whole trip. I realize it's too early to put the "done" stamp on this one, but it looks promising. I'll check back in a few days and let you know if the fix takes.

[Cadillac Jim]

That's good news. Let us know what you find out.

[human]

That's good news. Let us know what you find out.

Well, the fix didn't take. The problem still happens, but the dash lights do tend to stay on longer now (usually up to about 15 minutes) before the system reverts to Daytime Running Lights mode with dimmed headlights, no dash lights other than LEDs on the odometer, DIC, radio, and climate controls (I have an analog instrument cluster), and no interior lights when I park the car and open the door. The dimmed headlights go off immediately when I put the car into park.

Since replacing the relay, I have observed the following repeating symptoms:

1. The malfunction happens quickest when both the Twilight Sentinel and fog lamps are turned on.

2. The malfunction will hold off the longest when the Twilight Sentinel and fog lamps are off and I turn the headlights on manually.

3. When the malfunction occurs with the Twilight Sentinel on, I can manually turn on the headlights and and exterior lights with the pull switch, but the dash panel lights and interior lights stay off because the system has fooled itself into thinking it's daylight outside.

[Cadillac Jim]

The Twilight Sentinel is one of the electric eyes just behind the windshield in the center of the dashboard. These sensors are visible through the windshield when you lean over the hood as small holes in the padding. I have had service managers check out the twilight sentinel by placing a clipboard over it to see if the headlights come on. If you have anything on the dashboard, make sure that it does not obstruct the twilight sentinel. Having papers on the dashboard that cover the twilight sentinel could be the cause of your problem, now that you have fixed the inadvertent power problem.

The other electric eye is the sun sensor. It works with the A/C along with the interior temperature to determine how cool the air out of the vents should be. If you don't seem to be getting enough cooling on hot days, the sun sensor could be obstructed.

[human]

I think I know the sensors you are referring to. They're both made of purple plastic. One is dome shaped and the other is flat. Which is the Twilight Sentinel, the flat one or the dome? On my car, they're set into a piece of plastic that is also the defogger vent cover. The dash itself is slightly warped around the opening where this vent assembly fits, so doesn't sit flush in its slot anymore. Could this be contributing to the problem?

I think the sensor itself is working at least somewhat because at night the headlights will come on automatically when the Twilight Sentinel is on and the DIC will show the message "Headlights Suggested" when the Twilight Sentinel is off. Perhaps the warped dash has pushed the sensor to an angle where it's getting more light than it should or letting light in where it shouldn't penetrate.

Where can I find the part number for this sensor?

[Cadillac Jim]

I have my doubts that the sensor itself is the problem. I have a 1997 myself and have absolutely no change in the twilight sensor behavior since the car was new. I parked the car outside in the daytime until 2004, but indoors much of the sime since, so my senor may have seen less sun than yours, but we haven't seen any bad twilight sentinel sensors at Caddyinfo that I know of, and Caddyinfo is a pretty well-known and active go-to source for solving problems. I think that the sensor and/or windshield may need cleaning, or if you think that the dashboard has warped and is obstructing it you might rearrange things there. But, to answer your questions:

As best I can tell from the FSM, page 8A-201-27 figure 52, the Twilight Sentinel sensor, called the Ambient Light sensor in the figure, is the one on the driver's side and seems to be the one with the dome. If the sensor itself were bad you would likely see one of these codes:

B2419 Twilight Photocell Circuit Problem

B2641 Delayed Exterior Lighting Ctrl Circuit Range

B2645 Ambient Light Sensor Circuit

B2646 Ambient Light Sensor Circuit Range

B2647 Ambient Light Sensor Circuit Low (BCM)

Before I started taking the dashboard apart I would clean the senor with a soft cloth, using the same care as when cleaning a camera lens, and make sure that the windshield was clear of any contamination that might block light, inside and outside. Since it's got a dome, I suspect that it has a sort of fish-eye optic to get as wide a field of view as possible, like those door peepholes used in apartment buildings and hotels.

In the circuit, it should have a voltage between 0 Volts (light) and 5 Volts (dark) across it. Since yours is sensing dark all the time, I would check and make sure that the connector was fully engaged on the sensor, and that the wires weren't pinched or cut anywhere.

EDIT

The FSM page 8A-100-1 shows the schematic with the ambient light sensor. The wires to it are BLK and WHT and go to the Instrument Panel Cluster (IPC). This should help you determine for sure which sensor is the Twilight Sentinel sensor. The WHT wire is the one that will have 0 Volts to 5 Volts on it; the BLK wire is ground. The only other inputs are the wires from the driver controls, labeled "Headlamp switch" in the schematic. There is an off-on enable switch (the detent in the slider switch) and the slider switch position inputs. The PPL wire to the "headlamp switch" has the slider position voltage on it -- be careful, the PPL wire in most of the wiring harness is the network wire with the Class 2 Communications signal on it. The IPC and all of the modules have prominent warnings on the FSM schematics about being static-sensitive, and there are warnings in the FSM about "back-probing" connectors so use extreme caution when putting any test instrument on a wire that might be connected to the IPC or any other module.

[human]

I haven't seen any of those codes, so you're probably right that the sensor is okay. I looked on the underside of the sensors and the one with black and white wires is the flat one. The domed one has black and green wires. On both sensors, the wire runs directly into the sensor with no plug. I have no idea what the connectors on the other end of the wire look like. The dash and the sensors appear to be fairly clean.

This car was sold new in southern Florida and came north to the Carolinas about three years ago. so it's seen plenty of sun. As I think about it, the warpage of the dash is actually more of a slight shrinkage, which has caused the hole for the defogger vent assembly to pucker in the middle and push the vent assembly out.

I have my doubts that the sensor itself is the problem. I have a 1997 myself and have absolutely no change in the twilight sensor behavior since the car was new. I parked the car outside in the daytime until 2004, but indoors much of the sime since, so my senor may have seen less sun than yours, but we haven't seen any bad twilight sentinel sensors at Caddyinfo that I know of, and Caddyinfo is a pretty well-known and active go-to source for solving problems. I think that the sensor and/or windshield may need cleaning, or if you think that the dashboard has warped and is obstructing it you might rearrange things there. But, to answer your questions:

As best I can tell from the FSM, page 8A-201-27 figure 52, the Twilight Sentinel sensor, called the Ambient Light sensor in the figure, is the one on the driver's side and seems to be the one with the dome. If the sensor itself were bad you would likely see one of these codes:

B2419 Twilight Photocell Circuit Problem

B2641 Delayed Exterior Lighting Ctrl Circuit Range

B2645 Ambient Light Sensor Circuit

B2646 Ambient Light Sensor Circuit Range

B2647 Ambient Light Sensor Circuit Low (BCM)

Before I started taking the dashboard apart I would clean the senor with a soft cloth, using the same care as when cleaning a camera lens, and make sure that the windshield was clear of any contamination that might block light, inside and outside. Since it's got a dome, I suspect that it has a sort of fish-eye optic to get as wide a field of view as possible, like those door peepholes used in apartment buildings and hotels.

In the circuit, it should have a voltage between 0 Volts (light) and 5 Volts (dark) across it. Since yours is sensing dark all the time, I would check and make sure that the connector was fully engaged on the sensor, and that the wires weren't pinched or cut anywhere.

EDIT

The FSM page 8A-100-1 shows the schematic with the ambient light sensor. The wires to it are BLK and WHT and go to the Instrument Panel Cluster (IPC). This should help you determine for sure which sensor is the Twilight Sentinel sensor. The WHT wire is the one that will have 0 Volts to 5 Volts on it; the BLK wire is ground. The only other inputs are the wires from the driver controls, labeled "Headlamp switch" in the schematic. There is an off-on enable switch (the detent in the slider switch) and the slider switch position inputs. The PPL wire to the "headlamp switch" has the slider position voltage on it -- be careful, the PPL wire in most of the wiring harness is the network wire with the Class 2 Communications signal on it. The IPC and all of the modules have prominent warnings on the FSM schematics about being static-sensitive, and there are warnings in the FSM about "back-probing" connectors so use extreme caution when putting any test instrument on a wire that might be connected to the IPC or any other module.

[human]

I did a little experiment this afternoon and covered both light sensors with black electrical tape. With the Twilight Sentinel turned off, the "Headlamps Suggested" message appeared on the DIC. When I took the tape off, the message disappeared after a few seconds. I then tried covering just the domed sensor. No effect. But when I covered the flat sensor, the message returned. Now I know which sensor is the one for the Twilight Sentinel and I have established that it does function.

After it got dark, I drove around with Twilight Sentinel turned on, the fog lamps on (usually a worst-case scenario for this malfunction), and the flat sensor covered with electrical tape. I drove around for about half an hour, through a variety of ambient light conditions, including a well-lit parking lot, and the dash lights stayed on! Everything worked normally.

This leads me to believe the problem is in the sensor circuit. Either the sensor itself has become too sensitive to light or something is throwing the voltage off so that small changes in ambient light are causing it to go over/under the threshold and reverting it to daytime driving mode. The part that I don't understand is why it doesn't go back to night mode when I'm on a dark stretch of road.

After my little experiment, I had a hair-brained idea that I might be able to correct the problem by taking a sharpie marker and darkening the lens of the sensor a little. But which color? I want it dark enough not to be sensitive to streetlights, but not so dark that daylight doesn't penetrate. I'm thinking black would nt be the color of choice. It would be handy to know which part of the spectrum the sensor is most sensitive to. I'm going to try the tape thing for a couple more nights to make sure tonight wasn't just a fluke, then I may try pieces of transparent tape, colored over with various markers to see which one provides the desired degree of light filtration.

[Texas Jim]

I did a little experiment this afternoon and covered both light sensors with black electrical tape. With the Twilight Sentinel turned off, the "Headlamps Suggested" message appeared on the DIC. When I took the tape off, the message disappeared after a few seconds. I then tried covering just the domed sensor. No effect. But when I covered the flat sensor, the message returned. Now I know which sensor is the one for the Twilight Sentinel and I have established that it does function.

After it got dark, I drove around with Twilight Sentinel turned on, the fog lamps on (usually a worst-case scenario for this malfunction), and the flat sensor covered with electrical tape. I drove around for about half an hour, through a variety of ambient light conditions, including a well-lit parking lot, and the dash lights stayed on! Everything worked normally.

This leads me to believe the problem is in the sensor circuit. Either the sensor itself has become too sensitive to light or something is throwing the voltage off so that small changes in ambient light are causing it to go over/under the threshold and reverting it to daytime driving mode. The part that I don't understand is why it doesn't go back to night mode when I'm on a dark stretch of road.

After my little experiment, I had a hair-brained idea that I might be able to correct the problem by taking a sharpie marker and darkening the lens of the sensor a little. But which color? I want it dark enough not to be sensitive to streetlights, but not so dark that daylight doesn't penetrate. I'm thinking black would nt be the color of choice. It would be handy to know which part of the spectrum the sensor is most sensitive to. I'm going to try the tape thing for a couple more nights to make sure tonight wasn't just a fluke, then I may try pieces of transparent tape, colored over with various markers to see which one provides the desired degree of light filtration.

It sounds like you may have found the issue...I hope so.

I have been following this thread...it has been interesting.

A problem like that is so frustrating.

The transparent tape may be a good idea.

Just the tape by itself will probably block SOME light...and you could carry a roll of tape and a marker in the glove compartment to experiment with.

Sounds like an excellent idea to determine if "THAT" is really the problem.

The only strange anomaly that I noticed about your problem, was the inside dome lights.

I don't see where the Twilight Sentinel would have any effect on the interior lights.

I have a similar problem with my 2006...but it is EXACTLY OPPOSITE of yours.

Mine is not SENSITIVE ENOUGH to light.

It turns the lights on way before it is dark enough to need them and will not turn off till the sun has been up 2 or 3 hours but it has no effect on the interior lights at all.

Took it back to the dealer 2 times while it was still under warranty, and they said it checked out within specs and would not replace it.

Oh well...at least it isn't dangerous like yours is and I can live with it.

After 3 years and 70,000 miles, I have kinda got used to it.

Good luck with yours.

Keep us informed about what you find.

[human]

After using the electrical tape solution for a few days, I satisfied myself that the problem is the Twilight Sentinel's ambient light sensor is too sensitive. Whether the problem lies in the sensor itself or elsewhere in the circuit is still an open question, but at least I can treat the symptom.

Yesterday, I took the next step in my "band-aid" and created a colored "gel" using transparent packing tape and a magenta sharpie marker. I picked magenta more or less at random out of the handful of colors I had on hand. I stuck this over the sensor and everything functioned as it should with the Twilight Sentinel turned on. It stayed in daylight driving mode during daylight and in night mode after dark. Most importantly, the dash lights came on and stayed on after dark. I'm going to subject this fix to a little more long-term testing to make sure I'm satisfied with the results, then decide whether to continue with the tape or color over the sensor with the marker.

[Cadillac Jim]

This is truly bizarre. I have never heard of a twilight sentinel that was too sensitive to work properly before.

I have the idea from your early posts on this thread that your inadvertent power circuit was dead and had been for some time, and the twilight sensor sensitivity problem cropped up when you fixed that by changing the relay. Was the twilight sentinel sensor sensitivity always a problem, or did it come up lately? Was the onset sudden or gradual?

[human]

The onset was fairly sudden. My dad owned this car for the past three years and I've driven it quite often during that time without any trouble. He gave it to me about two months ago and the twilight sentinel problem cropped up shortly after that. It started out somewhat sporadically, but within the space of a week or so became very consistent. Some of my online research indicated the inadvertent power circuit could be related to the problem, and the relay wasn't very expensive, so I tried replacing it. In the end, that didn't really help.

The idea of the overly sensitive sensor turns out also to be somewhat overly simplistic. Covering the sensor is effectively treating a symptom, but not really solving the underlying problem. I say that because tonight I was out at dusk and the headlights and dash lights came on as they should with the colored tape in place, but one of my errands was to drop something off at my storage unit. To do that, I had to key in a code at the gate. I put the car in park while I leaned out the window to do that, and the headlights and dash lights went out. The headlights came back on when I put the car back into drive, but the dash lights stayed off. When I pulled around to my unit, I turned the car off and got out. The interior lights didn't come on. It took me about two or three minutes to do what I needed to and get back in the car. The interior lights still did not come on and I still had no dash lights all the way home, although by this time it was completely dark. I even tried putting the electrical tape over the sensor and that did nothing.

Covering the sensor does give me more control over the problem than I've previously had, and that's definitely a good thing, but it's by far not a comprehensive solution.

This is truly bizarre. I have never heard of a twilight sentinel that was too sensitive to work properly before.

I have the idea from your early posts on this thread that your inadvertent power circuit was dead and had been for some time, and the twilight sensor sensitivity problem cropped up when you fixed that by changing the relay. Was the twilight sentinel sensor sensitivity always a problem, or did it come up lately? Was the onset sudden or gradual?

[Cadillac Jim]

That's what I was looking for, evidence that there was another electrical problem. This is beginning to sound like it might be a bad ground under the dash. Keep checking the codes and let's see what turns up.

[Seanmannino]

I checked all the lights and everything is working except for the little red ones on the rear quarter panels. Are these lights or just reflectors? Also, the dome lights worked when I first the driver's door, but did not work while I was opening and closing doors as I checked the other lights.

It sounds like a bulb somewhere is shorted, or is shorting occasionally. This can happen with a broken or burned out bulb. Since it seems to be intermittent, you can start by turning on the parking lights and walking around the car. Don't forget the small bulbs in the running lights on the sides of the fenders, and the small bulbs near the license plates. Look at the bulbs in the trunk and under the hood, too. There are also two bulbs in each sun visor.

Not sure if this has been answered for you yet or not (haven't read entire post) but yes the little red "lights" in the rear quarters do in fact have bulbs in them one for each side to which a Sylvania 194 will work. only know this because I just replaced mine.

[human]

Thanks for your input. I hadn't yet determined whether those were lights or reflectors. I'll check the bulbs.

I pulled trouble codes yesterday and the only active ones are

-MMM B2148 and MMM B2150. These relate to the vertical and horizontal position sensors on the passenger side rear view mirror, which I replaced after I broke the original one in a bank drive thru. The replacement mirror is a basic one, not heated or self dimming, which the original one was. so there's one mirror wiring harness that isn't plugged in.

A few history codes are also showing up:

-PCM 0300 (engine misfire. I replaced the ignition coils and it now runs smooth as silk)

-PCM 0503 (Cruise Control failure. happened once the day I got the car and never happened again)

-ACM B1340 (Air Mix Door Movement Fault. There's a blend door that's constantly creaking back and forth. Been doing it for years)

I checked all the lights and everything is working except for the little red ones on the rear quarter panels. Are these lights or just reflectors? Also, the dome lights worked when I first the driver's door, but did not work while I was opening and closing doors as I checked the other lights.

It sounds like a bulb somewhere is shorted, or is shorting occasionally. This can happen with a broken or burned out bulb. Since it seems to be intermittent, you can start by turning on the parking lights and walking around the car. Don't forget the small bulbs in the running lights on the sides of the fenders, and the small bulbs near the license plates. Look at the bulbs in the trunk and under the hood, too. There are also two bulbs in each sun visor.

Not sure if this has been answered for you yet or not (haven't read entire post) but yes the little red "lights" in the rear quarters do in fact have bulbs in them one for each side to which a Sylvania 194 will work. only know this because I just replaced mine.

[human]

Things have been operating more or less normally for the past few weeks. I changed the piece of colored tape over the sensor from magenta to dark blue and I pretty much have dash lights when I should, but today my girlfriend and I took the car on a day trip to the mountains, and I had a bit of trouble. We watched a beautiful sunset from an overlook and then headed back to a nearby town for dinner. The steep and winding road was very dark and I had the headlights and dash lights functioned normally until we got into the town. As soon as we got to an area lit with streetlights, the car reverted to daylight mode (dimmed headlights and no dash lights) and would not go back to night mode, even when my girlfriend held her hand over the sensor for a couple of minutes. After dinner, we headed home and everything worked fine until we hit a stretch of highway on the edge of our city, which was heavily lit with orange streetlights. The car again went to daylight mode and would not return to night mode, even when we went through a very dark stretch of highway for about 10 minutes. In both cases, I turned the headlights on manually with the dashboard pull switch to return them to proper nighttime intensity, but the panel lights did not come on.

The new piece of information I learned from this is that once the lights are in daylight mode, they will not go into nighttime mode until the car is turned off for several minutes and the system can reset itself. Other Twilight Sentinel-equipped GM cars I've owned have had a tendency to go in and out of nighttime mode with great regularity, even when driving through patches of shade and sunlight along a tree-lined street on a summer afternoon, reacting to the changes in ambient light within a second or two.

[human]

I got very frustrated a few days ago when I was running errands on a gloomy, rainy afternoon. I felt I needed dash lights, so I put a piece of black electricians' tape over the light sensor to force them to come on by tricking the car into thinking it was night. Of course, I had to park the car, run into a store, and come back about 10 minutes later before the system would reset itself. After that, I had full manual control over lights and dash lights as long as I left the twilight sentinel off and the fog lamps on. In that configuration, I have parking lights and fog lights with the car in gear and the headlights turned off manually, but no headlights in daytime running mode. If I turn the fog lamps on, the headlights come on in daytime running mode and I get a "headlamps suggested" message on the DIC. That message does not appear with the fog lamps on.

I can live with things like this. I'm not fond of it, but I can live with it. At least I can now control the dash lights. Any further insights would be appreciated.

Update: This evening, while running errands I parked in front of a vacant store to make sure my headlights were functioning properly in this new configuration. There's one anomaly: When I turn on the high beams, not only do the fog lamps go off, but so do the low beams. Correct me if I'm wrong, but I don't believe it's supposed to do this. I think the high beams are supposed to come on in addition to the low beams. Does this information provide anyone any insights that might be helpful? If so, do tell.

[gamefanatic]

I just had a similar problem with my Seville '97. In my case this problem had become a problem more and more over time. If I placed something over the sensors the lights would turn on. This was especially problematic in low light situations, where I could see outside, but barely see the deep dash console. Finally tonight the lights would not come on and it was pitch black outside.

After going through this post and the IPC, I found that the IPD07 value's were "lower" than needed. The max value was around 115. If you pull the Sentinel (Ambient Light Sensor) the reading jumps to 255 acting as if it were pitch black outside. I have a '99 spare parts car, which I replaced the sensor with. It appears that much like a Christmas tree light it doesn't matter which way the sensor is plugged in. Also I wanted to note the focus hole on the '99 sensor was slightly larger. So far so good! Hope this helps someone else with this problem! =)

BTW AllData is useless for getting information on this... Recommend the FSM!

[Cadillac Jim]

Thank you for pitching in.

I've re-read this thread and would like to point out that something that can cause a similar problem with no codes is a bad contact on one of the terminals in the connector to the headlight switch. If one of the connectors to the slider switch for the delay is not making contact, or it's intermittent, you can have problems that look like an intermittent twilight sensor.

[human]

Wow, diggin' up an old thread!

I don't own this car anymore, but I did finally solve the problem a few months before I sold it. About a year ago, I pulled the twilight photocell out and left the socket empty. Suddenly, I had a fully manual headlight system with working dash lights! Last fall, I was at a junk yard getting a few parts for the Pontiac Bonneville I bought to replace the Caddy and pulled a twilight photocell out of a Bonneville. I plugged the cell into the Caddy when I got home and full automatic function was restored. I just wish I had known to do that--or at least pull the photocell out--about a year earlier. I would have been a much happier camper.