This is gonna sound weird but stick with me. This happened to me. The tail light and brake lite ground circuit is really wonky if you don't understand it. I've studied my wiring diagram until my eyes glazed over and I still don't understand it.
Anyway to the point. Check every bulb on the truck. Ensure you can actually remove the bulb. I had a reverse light bulb where the glass actually turned inside the brass "cup or base" and the filament was shorted to ground. You couldn't tell by looking at it and the odd thing was the bulb out up but the brake lights were acting weird.
It's worth checking.
So yer saying, a hosed up bulb or electrical connection somewhere else could be sending stray voltage through the entire truck and only lighting up the dome and courtesy lights specifically?
I'm tracking, sort of, and not too many lights left to check that out. Tail/brake/reverse lights all work good and recently cleaned up from the PO using axle grease as dielectric...no comment
I can check the posers and front turn signals easy enough. Both of which work fine and this "short" happens even when no power to any of the other lights and other lights on or off don't affect it's condition. I tried that, turn everything on/off to see if something else random is going on and nothing found.
Cargo light works fine and is clean too. In fact, save for this stupid dome light thing, literally every electrical device and gauge on the truck works flawlessly. Save for a couple burnt out dash cluster bulbs. They not very bright but they do dim with the headlight switch like they should. BTW, no blown fuses either although I did touch hot to ground popping out the old dome bulb once when it was shorting and it blew the fuse under the dash just like it should...and now its fine w new fuse.
BUT should the cargo light ONLY work from the switch up on the B pillar or should it work only IF the dome light is on (ground circuit completed by any of the 3 switches)? I'm going to pop up a wiring diagram I found, still haven't pulled out the old haynes or chilton books I got somewhere.
Looking at that diagram, cargo lamp ground is tied to the ground wire from the dome/courtesy/switches. And the + wire runs through the b pillar switch.
IE cargo only works if dome light on AND cargo + switch on.
Currently (no pun intended) the cargo light works with the cargo switch but don't turn off (sometimes? maybe) when the door shuts/dome light off.
The problem might be in the cargo lamp. It has a metal housing and the gasket is pretty, very, crusty between it and the cab.
I may have fingered it out?
If one of you guys figures this fcking puzzle out though, I'll send you a square body memorabilia! I have a spare hood ornament.. actually 2, now that it's a GMC and not a Chebby....
