Lostpatrolman

iTrader: (3)

I just bought a 98SS convert. The courtesy lights are not working. I checked the fuse and it is good. The reading lamps will work if I turn them on manually. I checked voltage to the rear lights, and they are not getting power. I thought the problem might be the door switch, but the lights wont turn on when I open the trunk, or unlock the car either. Is there some sort of relay that needs to be replaced?

Lostpatrolman

iTrader: (3)

anyone?

WhiteBird00

iTrader: (4)

There is no relay - the courtesy lights are controlled by the BCM. I would double check the COURTESY fuse or even put a known good one in its place. I've seen several instances (even just last week) where the courtesy lights weren't working with an apparently good fuse that turned out to be the fuse after all.

Does the glovebox light work? It's on the same circuit. If it works then you need to check for a break in the white wire that goes to position D1 in the 32-pin blue connector at the BCM. This is the ground wire for the courtesy lights. The glovebox and the map lights have an independent ground for manual operation but all the courtesy lights ground to the BCM during automatic operation. This allows the BCM to create the "theater dimming" effect. An easy way to check is to use a jumper wire to ground the white wire and see if the lights work (except they won't shut off when not connected to the BCM). If they work then the wire is not broken and you have a problem in your BCM. If they don't then you'll have to track down the break in the wire.

Lostpatrolman

iTrader: (3)

Yes, glovebox lights work. Where is this white ground located? Are there some wiring schematics on the web anywhere?

WhiteBird00

iTrader: (4)

The white wires run from each of the courtesy lights except the glovebox to the BCM. The BCM is a black box about the size of a paperback book that is mounted under the right side of the dash behind the glovebox. You will find it has three plugs - a 6-pin black, a 6-pin green and a 32-pin blue. The white wire is in position D1 of the 32-pin blue connector. That is the first position of the bottom row when you look at the "business end" of the plug with the locking tab positioned at the top.

Also, try turning the instrument panel dimmer all the way on and let us know if the lights come on.

Lostpatrolman

iTrader: (3)

I already tried the dimmer too, it didnt turn them on, same thing with hitting unlock, opening the doors, opening the trunk... It must be the ground, or the bcm itself. I guess i will dig into it. Thank you for your help. Also, once I find D1 i should be able to probe that wire and the courtesy light itself to make sure the line isnt broken right?

Lostpatrolman

iTrader: (3)

Ok, Im confused. I jumped a ground wire to the ground side of one of the rear lights and all my lights illuminated like they are supposed to. When I took the ground wire back off, the lights stayed on. They did not shut off until I closed all the doors. They would not have done this if I had a bad ground, right? What does this mean? Is my bcm bad?

Lostpatrolman

iTrader: (3)

Whitebird, have any more suggestions?

WhiteBird00

iTrader: (4)

It sounds like the BCM might be the culprit. I checked the service manual but couldn't find confirmation of what I suspect. I think what is happening is this... the BCM provides both ground and power to the courtesy lights. If it turns on the power but gets no return signal on the ground side then no current flows and the lights don't work. By providing an independant ground you "kick started" the BCM to provide current through the power circuit which then continued through its own ground circuit even when you removed the separate ground.

You can test this with a test light or multimeter. Access the BCM behind the radio and check that you get power on the dark blue with white wire in the black 6-pin connector when the door is opened. This is the courtesy light feed wire.

While you're there, check that you have battery power at the orange wire in the same connector. This is the input power from the COURTESY fuse in the fuse panel.

If you have input power on the orange wire but no output on the dark blue with white wire then it's a pretty safe bet that the BCM is the problem.

Lostpatrolman

iTrader: (3)

Thank you. I will try that.

WhiteBird00

iTrader: (4)

I just realized that I made a mistake in the previous post - the BCM is behind the glovebox not behind the radio (the DRL module is behind the radio).

GMendoza

iTrader: (2)

Alright!! I'm bringing this back from the dead!!!

Whitebird, I don't understand this test. If the lights turn on by jumpering ground to the white wire, then it's safe to say both power sources are working. The issue is the BCM is not providing ground through the white wire.

If all other acc that require ground are working, then its safe to assume BCM is grounded and the BCM is bad by not providing a courtesy ground. Do you agree?

Also, has anyone succesfully repaired the courtesy issue in the BCM?

Topless TA

iTrader: (10)

good question i am having the same issue.

Esoteric[TG]

I'm with topless TA, does anyone have an answer to this question? I'm on my 3rd or 4th fuse this week, they last a couple days and then pop.

WhiteBird00

iTrader: (4)

The test is valid but the reasoning behind it was not clear. The BCM provides power for both the courtesy lights and the map lights via the dark blue with white wire. This power is constant (battery) and is available at all times except after the BCM has initiated its battery protection mode. The battery protection mode shuts off the courtesy lights after about 10 minutes to prevent battery discharge in case a door inadvertently gets left open.

The map lights have their own ground through the map light switches on the mirror to the black wire. The courtesy lights ground through the white wire to the BCM. The BCM varies the available ground on the white wire to provide the theater dimming effect and to turn off the courtesy lights while still maintaining power for the map lights.

The power gets to the BCM via the COURTESY fuse in the dash fuse panel. My suggestion to use a meter to check for power on the dark blue with white wire works but isn't necessary. Merely turning on the map lights will tell you if you have power there.

BCMs have been known to develop cracks in their solder joints resulting in intermittent power problems for the RAP circuit (radio and windows). It is quite possible that a similar problem could be affecting the courtesy lights. However, I don't have any internal schematics for the BCM so I can't tell you exactly where on the board to look.

Esoteric[TG]

First off, thanks for answering back, its nice to deal with someone who actually has a handle on wiring things.

Now, if I'm understanding what your are saying, the BCM could cause the lights not to work, but it would not cause a fuse to blow?

I'm losing my courtesy fuse on a fairly regular basis, and it only seems to happen when the door is open (courtesy lights are on) It ends up being kinda annoying, I could live without the lights, but I do miss my keyless entry.

Thanks in advance for your help.

David.

WhiteBird00

iTrader: (4)

Any electrical device can cause a fuse to blow. It is quite possible for the BCM to do this - it's just not very common. And it's hard to diagnose especially when it's an intermittent problem.

If it happens fairly regularly then it might be worth substituting another BCM as a test. If you know someone with an 98-02 f-body, maybe you could swap their BCM. The car won't start because of VATS but the courtesy light functions will work so you can check if it blows a fuse. That should confirm or eliminate the BCM as the source of the problem.

Esoteric[TG]

Thanks for the reply, I'll have to try to find a BCM to swap out for a quick (ish) test.

I really appreciate your help. I'll experiment and report back when I have something to say.

David.

Esoteric[TG]

Now a new wrinkle. It looks like the issue has gone from intermittent to constant. Its irritating, but now at least I should be able to experiment and find the cause.

The other symptom I'm having is a click from the BCM area that occurs about every 10 seconds when the key is on.

I'm going to spend some more time tracking through the circuits, but I was hoping this might ring some bells.

Thanks again for all your help.
David.

Esoteric[TG]

Well, I figured mine out. I guess I really should have been following the "check any recent mods" advice...

Turns out it was my fault all along. I installed a homelink module about 3 months ago, and somehow the wires ended up shorting out. I found burn marks on one of them so it looks like it was my fault all along.

Thanks for your help WhiteBird00.
David.