Bizarre stoplamp problem

SnakeEyeSS · September 28, 2014

2007 Tahoe LTZ

I changed the battery a few weeks ago, only recent thing done.

The related fuses look perfect. The bulbs looked good but I replaced then anyway.

The problem:

The left stoplamps,(taillights work when lights are on) the right bottom stoplamp, do not come on.

The right top stoplamp works, as well at the third brake light(LED strip above rear window)

The turn signals work(just the lower blubs flash with signals, is that right? I can't remember, rarely behind it)

I have read there is some kind of wiring relay box behind the bumper that is a common problem on these?

This is sadly looking like a go-to-dealer problem?

MikeNH · September 28, 2014

You could poke around looking for a damaged/loose ground but the first step in trying to diagnose this without heading to the shop is to find a wire diagram.

SnakeEyeSS · September 28, 2014

I just spent many many hours chasing a wiring problem on another car. REALLY not in the mood.

The sides are wired separately, judging by a fuse for each side, so I am having trouble thinking it could be a single harness past the fuse box. Itvwould have to be that just the pins related to those three light bulbs. have an issue. Really hoping its not electronic. A new battery shouldn't have damaged the BCM, that's what the fuses and relays are for.

SnakeEyeSS · September 28, 2014

Think I'm going to try this later. Probably not the problem since one light still activates, but it's a cheap part.

http://www.gm-trucks.com/forums/topic/120988-2008-cruise-control-problems/page-2

Well, my cruise works fine so I doubt that is the problem.

SnakeEyeSS · September 28, 2014

Front drivers side DRL isn't working either. Filament is unbroken.

gmtech4 · September 28, 2014

You need a schematic before even thinking about doing anything else ,,,,,,, and some reading between the lines skill

SnakeEyeSS · September 28, 2014

Wow, fixed it. Ended up still being bizarre.

I had put a new bulb in and nothing changed. Still bugging me so I changed the DRL blub hoping it wasn't related, that was just a bad bulb(figured I would save on some diagnosis there), so that was solved.

That encouraged me to try the same thing and expect different results, so I took the known good bulb (used) and started plugging it in in other spots.

Stuff worked with that bulb. I plugged new bulbs in the problem area and it started working.

What are the odds of one filament only in three dual filament bulbs in different spots going bad within 3 or 4 uses?

Anyway,

One of two things happened that threw me off earlier, I lost track of the new and old bulbs, or one of the new ones was bad.

How could I lose track of a bad bulb?

The strange thing, only the DRL bulb had any sign of a problem. The back bulbs had intact filaments, no burn marks inside glass or on contacts, and the silver stuff below the filaments attach points that turns black when the bulb goes was still silver. Never seen that before, I've always found even a small sign or hint when closely examing a bad bulb.

I think I've been scared by my other electrical hunts recently(took days of tracing wires, looking at diagrams, and testing circuits), and started over thinking it.