Sxxx is a splice location where wires on the same circuit come together. SPxxx is the designation for a splice pack where the wires come into a connector that then on the other side completes the splice. Splice packs are typically used for major ground locations so that circuits can be broken apart and isolated for testing.

Now, the operation of the courtesy lamps in your truck happens in this manner. The +12V power is supplied directly to the lamps. That is supplied through the CTSY fuse. The courtesy lamp relay then completes the ground side of the circuit when commanded to by the BCM (either when the door switches close the ground loop back to the BCM or when any of the other inputs the BCM uses are triggered).

So your problem is with the white wires from the overhead lights grounding out somewhere between the courtesy lamp relay and the lights themselves. Since they are all in series (splices between the relay and the lights), a grounded out wire at any one of the lights or anywhere in between would cause them all to illuminate.

 

I'm willing to wager that I was wrong, the schematic didn't make sense because it appears that the lights are between power and ground.

So I decided to try something, unplug the lights one by one and see what happens. Using a voltage tester, see if there is power still there without a light. Since the rear light would be hardest to reach I went to undo that one first... when I pulled it out I noticed that there was some bare wire showing on the white wire. Odd...

I closed the latch and shorted that bare wire to the frame... the lights came on. I actually remember causing this injury while installing my XM antenna.

Live and learn.

Thanks for the help Kyle.

Jim

 

That would definitely cause it! Wrap that wire and see if the problem persists.

 

If I did it right, here is a blurry picture of that little devil, but you get the idea.

 

Im having the same problem, i somehow flipped the rear light switch and it stayed on all weekend (obviously draining the battery) i charged the battery up then realized that the switch was on so i turned it off and the other two forward dome lights stay on now. so im assuming the problem is back there somewhere so ill take a look.

So did you just take that rear light out?

ill keep everyone updated. i thought i would post my problem here just in case my problem is different, so other people who might have this problem will have more info.

Ok well i found the problem, pretty much the same exact problem you had. in one spot by the light the white ground wire got pinched in between the metal and the trim, so i guess it just finally rubbed enough of the insulation off. so i wrapped electrical tape around it and all is well.