fuel pump harness. scratching my head

[rockfangd]

Hi all. I ran into this issue with both of my 97 Cadillacs. Somehow I must have got it right on the Deville but want to be sure it is right for my Seville.

They had the harness issue and you have to replace the square plug with the flat one.

There are 4 wires

gray. fuel pump +

purple. level sender signal

black

black.

The issue I am running into is the 2 blacks. would be pins C and D on the square plug.

One of the blacks is for the fuel pump

and one is for the sender.

both blacks are the same diameter so that is no help.

Not sure if it actually matters which goes where.

But pin D is burnt on my square plug which makes me think it is the fuel pump ground.

I wish it had the black/white like they usually do.

Anyone who can help I would really appreciate it.

[Cadillac Jim]

I looked in my old paper 1997 FSM and have the linear connector for the fuel pump connector. I can get more data on it if you like. From your diagram and description, and from the FSM schematic on page 6-254 I can give you this:

The GRY and BLK wires are the fuel pump power and ground. The BLK wires goes through connector C415 to ground G401. The GY wire goes to the fuel pump relay, pin A1.

The PPL and ORN/BLK wires the fuel level gauge signal and reference. These both go to the IPM.

Yes, one is not really a ground; the ORN/BLK wire won't carry enough current to support the fuel pump. The use of the PPL and ORN/BLK wires *only* for the fuel level gauge are essential for consistent and accurate fuel level readings. It matters very much which goes where.

Hope this helps. I'll have more time tomorrow if you need more details.

[rockfangd]

Ok so If you look in the pictures I posted it looks like I have it wired right so far.

The black that is left over goes to the org/blk.

Why would that wire be burnt? If all it is for is the fuel gauge where would it see enough resistance to get that hot?

that is mainly what threw me off. (referring to pin D in the square plug)

[Cadillac Jim]

I was about to leave the house with the previous message. Fixing a typo, the fuel pump and relay schematic is on page 6-264. The fuel gauge is on page 8A-51-1 in the Body Control Module schematic.

I'm a little nervous about the burnt wire. So, I'll collect all the data, then look at your figures and the data. For a first cut, the fuel pump is on the larger AWG 16 wires in the center two terminals of C415, and the fuel gauge is on the smaller AWG 22 wires on the end terminals. From your connector diagram, the big wires and little wires are in an X pattern, not on each side of a square.

The wires:

FSM Page Color Wire size Circuit FP/PZM C1 C415 Term Connection
6-264 GRY 1 120 B B Fuel pump POWER
6-264 BLK 1 1250 C C Fuel pump GROUND to G401
8A-51-1 PPL/WHT 0.35 30 A1 A Fuel gauge REFERENCE
8A-51-1 BLK 0.35 552 D8 D Fuel gauge RETURN

NOTE that the C415 terminal designations and the rest of the designations for the fuel pump power wire all through circuit 120 are different for the 1996 model year, for some reason. This is marked, with 1996 model year data, in the 1997 FSM.

C415 is the connector at issue here. End view is on page 8A-202-29 and is shown without a table. The terminals are labeled A-B-C-D from right to left with the connector clamp DOWN; this is part number 12129565; figure:

Another photo:

For the other connector, the terminals are labeled A-B-C-D with the connector clamp UP; this is part number 12129600.

End view figures:

G401 is under the rear seat on the right side, on a bolt to the rear of the seat support member (8A-201-43, Fig 78).

For some reason, the wire sizes are given in square mm. I guess that's the metric way. AWG sizes are given in Figure 6 on page 8A-5-4:

Metric Size (mm squared) AWG Size
0.22 24
0.35 22
0.5 20
0.8 18
1 16
2 14
3 12
5 10
8 8
13 6
19 4
32 2

[Cadillac Jim]

Several things come to mind looking at your diagram and photos, after piking parts of the FSM to post. First, all four of your wires look like the same size, and they all look like AWG 22 (small); you noted that problem on your first post. That could be because the newer, tougher plastic insulation makes wires look a lot smaller than the older plastic insulation, but I don't think so. I think that somebody decided not to use AWG 22 wires when they were building the harness.

The ground wires *should* have been BLK and ORN/BLK. You noted this in your first post, too.

I think that the old wiring crossed over the two grounds because I can't see a fuel gauge return or reference line burning anything. Note that in your last photo, against a denim background, that one black wire *does* look a little smaller than the other black wire. The small black wire should go to the orange and black wire, or, in the photo, apparently the orange wire. I don't see A-B-C-D corresponding to PPL/WHT-GRY-BLK-BLK, or the AWG sizes big-small-small-big.

[rockfangd]

Ok so I took a picture of the plug under the car and it helped alot.

Makes me question if that whole plug is meant to be cut out and only have one plug to the module.

The one on the far left. (the small black) is the one that is burnt. No clue why. I noted that the fuel pump had been replaced before so I am thinking the wires were mixed up at the pump module.

That is the only reason I could think that the pump failed and the wrong wire was burnt. (it was getting its ground from the wrong wire)

Another question. Does anyone know where the pads go on top of the tank. I want to put them back in place when I put the tank in.

Thank you very much for the help

[Cadillac Jim]

In this last photo, I can see a distinct difference in the wire sizes. The fuel gauge wires at the ends are definitely a bit smaller than the pump wires in the center.

I never dropped the tank on my Eldorado so I can't help you with the location of the pads. Lots of people here have dropped the tank on a 1997 Seville/Eldorado/Deville or equivalent, so I'm sure someone will chime in.

[rockfangd]

I have dropped enough of them but every one of them have been loose and dropped into the dip portion

[Cadillac Jim]

If nobody chimes in, I would position them centered so that the tank is stable when pressed against the body.

[rockfangd]

I remembered when I installed the tank today that there are marks on the tank where they are to be positioned.

I got the pump and tank installed today. I just have to put in the filler tube and hope to have it running by this weekend

[Cadillac Jim]

Thanks. This saves me the foraging through the 1997 FSM. Pipe up if you need anything.

[BodybyFisher]

I replaced the fuel pump in my Monte Carlo last year and it came with an upgraded connector, I think some of them were melting. I had to cut off the old connector and install a new plug that came with the pump, a different configuration altogether. The instructions were very clear and I soldered, shrink wrapped and taped the splices.

I would imagine that replacing it again after the new connector things could get a bit confusing

[rockfangd]

The W-body was pretty easy but Cadillacs have a short harness between the body harness and tank.

[BodybyFisher]

The nice thing about the Monte Carlo (W Platform) was that you could access the fuel pump in the trunk it made the entire job easy.

[rockfangd]

Well I finally put gas in it today and it fired right up.

Job was not bad at all.

I am so happy there is no rust at all underneath.

There is something that worries me just a little though.

When I first fire it up after storage it will tick for a few seconds, and also once it starts to warm up it ticks. I am pretty certain it did this last year too but as soon as I started driving it normally it was fine. I am going to be doing another oil change on it before I drive it for the summer. Going to run rotella in it.

I will be very upset if the tick does not go away but I believe it will.

I only put around 3000 miles a year on it so it.

hopefully it will warm up again in the next few weeks so I can start driving it again. Needs a good bath

[Cadillac Jim]

Congratulations on your patience, and your success.