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88 Eldorado headlight / dash lights problem


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Hello everyone! I recently purchased an 88 Eldorado and I am having problems with my headlights, parking lights, and dash illumination. When turn on the parking lights or headlights with the switch, the idiot light comes on and the digital dash and radio and DIC displays dim like they are supposed to, but the parking lights do not come on, nor do the dash lights for the radio and switches. However, when it is dark enough for the twilight setting to work, the headlights function perfectly on their own and my dash illumination works as well.

The owners manual for my car is missing, but I have checked all of the fuses (the glove compartment fuse block, under the hood, and the few that are under the dash on the passenger side near the relays), and they were all good, swapped them around with fuses of the same amp as well in case one was bad and I could not see it. I also purchased a new headlight switch thinking that it was the culprit, but no such luck. I have swapped all of the relays under the dash around and that did not change anything either, but like I said I do not have a manual and could not find anywhere online what relay is for what. The only other thing I could come up with would be the BCM, but I would hate to buy a new one if that were not the problem. Are there any other places that I need to check for relays or fuses? What else should I look for that could be the problem?

Also I checked for codes on the DIC and cleared the history of ECM codes and have not noticed anything re-appearing. When going through the DIC data, there are listings about headlights, are there changeable options in those settings? Does the factory manual explain all of this, or is there a place that I can read up about it?

Does anyone know what my problem could be? You help is much appreciated.

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I strongly suggest that you get a factory shop manual for your car. No aftermarket shop manual compares in any way to the comprehensiveness, completeness, or accuracy of the factory manuals. Nowhere else will you find a complete, comprehensive, accurate set of diagrams of the electrical system, with troubleshooting charts and repair instructions. These are the books that Mr. Goodwrench trains with, and uses as a reference when the car comes in for service. They are available from the GM source, Helm, Inc. but you should be able to get it faster and cheaper on eBay.

Fusible links are usually exposed single wires, not embedded or wrapped in a wiring harness. They usually have one end on a power source, like the battery cable or the fuse block. The wire color us usually red. You may be able to recognize one by the fact that they are a smaller wire of length of anywhere from a few inches to about a foot that is spliced into a larger wire.

There may be other fuse blocks in your 1988 Eldorado; I don't know because I don't have any information on the electrical system for that model year. Most Cadillacs of the 1992 model year and later do have fuse blocks behind the back seat that are accessed through the trunk. I recall some models of older cars that had fuse blocks under the back seat, which could be accessed by popping up the seat cushion, or pulling forward the back cushion. I have heard of fuse blocks in multiple places under the hood, in or behind the glove box, under the dashboard, under the seats, and in the trunk.

Relays are usually associated with the larger fuse blocks. Relays are used with high-power items like headlights and other exterior lights, power windows and seats, etc. You can mix-and-match relays of identical part number to troubleshoot which one has a problem, if any.

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