1990 Cadillac Deville 1990 Cadillac Devile NO LIGHTS TO THE

WILCOM1

MEMBER
1990 CADILLAC DEVILLE
V8
FWD
AUTOMATIC
103,000 MILES

I have a 1990 Caddilac sedan deville I have 3 open ckts. No fuses are blown so we aren't shorted to ground anywhere. Every other device and light on the car work as they are supposed to, just all lights to the rear are out. I have power to the antenna, it works fine. I also have power to the trunk closure, it works fine. What I am missing is the voltage on the BROWN wire to the tail, license plate and marker lamps, I'm missing the voltage to the YELLOW left and right blinkers and I'm missing the the back up lights which are the light green. These are from multiple sources. Light switch for the tail and marker lamps. The gear selector for the back up lamps and the blinkers that end up at the flasher thru the turnsignal switch. With opens from 3 directions, seems that a mid way connector hiding somewhere is my villian. I initially thought I had a bad body ground which would explain 3 different things going bonkers at once, but NO, I have ground everywhere. I have checked the connector under the rear bumper and the wiring harness that feed all the lights in the rear, all good, is there another connector b4 it gets to the front? Arrrrgh

5 Replies

FACTORYJACK

MECHANIC
4,159 POSTS

I see your dilemma, and I will get back to you after some research. Tonight was a busy night, and I am just tying some loose ends right now. I have access to a factory service manual for your vehicle, and if you don't hear from me through the afternoon, it will be tomorrow evening at the latest.

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Wednesday, March 17th, 2010 AT 11:38 PM

WILCOM1

MEMBER
3 POSTS

Thanks I appreciate it. I am trying to find out if the BCM would be in the ckts, I read where the BCM does conrol/have to do with the "exterior Lighting". My schematic does not show the BCM on the darn thing at all and I am having trouble seeing why the BCM would be in either of my ckts.

I did have the BCM replaced at the dealer a couple of years ago when my dash lights and fan motor went crazy, but why on earth would a BCM want to monitor or be in a tail light ckt? It makes no sense to have a BCM setting in the middle of my back up lights, what would it do with the it? Why would it want to monitor it? Would just ad complexity without much use, seems to me

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Thursday, March 18th, 2010 AT 12:56 AM

FACTORYJACK

MECHANIC
4,159 POSTS

The BCM is not part of the exterior lighting circuits on this vehicle. I did some research, and photocopied some information for my reference as we go along. In looking at the schematic, all of the affected circuits you mention share a couple things in common. But first, I need to establish some knowledge of what you've done so far. How have you determined these circuits have no power, was it with a test light? That would be the simplest of methods, and perfectly capable. One thing to consider is, was the test light working when you tested? If you have a poor ground to the light, or you don't function check it on a known good circuit to see that it lights, it can give you wrong info and send you on a goose chase. So, if it is a test light, you need to make sure it is functioning, and can be trusted at the time of testing.

Where did you test to determine that no power exists, at the sockets? All the circuits you mention, as I said, have a couple things in common. The all pass through connector C400, which is shown to be a 6 pin connector that is in the trunk behind the RH(passenger) wheelhouse. I don't have an end view that shows all the wires, but I do show by schematic info that; Pin A yellow, Pin B dark green, Pin D brown, Pin E light green, and Pin F is black. Pin C is unknown, and may be empty, but regardless, all the circuits pass through C400 so check it.

You mention that you have ground everywhere, How was this checked? The reason I ask is that all these circuits share a common ground, with exception of he LH rear side marker, which grounds at G200 at the left I/P shroud for some reason. The ground they all share is G402, which is in the RH rear of trunk, on rear of the wheelhouse, and probably next to C400. Check that this ground is clean and tight.

If this don't point you to a cause, then it will be down to checking wires. I have a hard time believing that you have three open wires, unless they are cut where they route together as a harness. That is if you truly have no power, and the ground is good. If you have a 194 bulb, place it in that left rear side marker lamp and see if it works. The brown wire that feeds it does not pass through C400, and like I say it is grounded at G200, which also, for the sake of reference, grounds your turn signal indicators in the cluster. I think you're going to find your problem at C400, or G402, though.

Good luck, and let me know.

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Thursday, March 18th, 2010 AT 11:05 PM

WILCOM1

MEMBER
3 POSTS

Thanks for your input.

I'm an telephone/ electronics tech and have a pretty good understanding of battery and ground. I tested the ground on the sockets with a multimeter and used the bumper as my source for continuity. I used a multimeter to check for voltage also and again I used the bumper as a ground reference.

I will recheck that 6 pin connector in the right wheel house again. It is actually located just outside the trunk by the tail pipe under the bumper. The only wiring going into the trunk was for the antenna control ( which does work).

Thanks again.

PS. Does your GM manual show the routing of the harness to the dash. I did a initial check and couldn't make out where the rear wiring harness takes off and heads forward.

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Thursday, March 18th, 2010 AT 11:31 PM

FACTORYJACK

MECHANIC
4,159 POSTS

I don't know what connector your testing at, but C400 is in the trunk. Have you pulled the lining away from the sides to expose the wheel house? The harness should run down the door sill, I would speculate the left side. Come up under the rear seat cushion and enter the trunk. It will exit the trunk through individual pass through grommets. It sounds like you may be testing at one of the rear lamps, to body harness connectors.