Help me fix my brake lights c1500

I'm going with a DPO "fixed" the trailer lights at some point.

I don't think this is your problem, but worth mentioning:

Have you confirmed that the bulbs are the correct bulbs and in the correct location/socket?

I'm just thinking there's an outside chance that a multi-filament bulb...the wrong one, is in a socket and causing some whacky back-feed scenario.

If not that, I agree that a test-light is your most useful tool.

A power probe gets rave reviews from all my customers...but I don't have one yet.  I've used the improv/poor-man's approach by using a battery (or low-amp trickle charger) and assorted lengths of wire and aligator clips.

In reply to ClemSparks :

Max points for the farnsworth picture.

I believe I do have the correct bulbs. If not I have taken out all other bulbs and the brake lights are still on.

Well after many hours of messing with this problem I’ve decided to throw up the white flag and outsource the repair.

This is not my daily, it’s supposed to be fun.

I had a similar issue in my 89. Ended up being the ground pin on the harness side. It had corrodedwith the circuit board and was toast 

So while walking the dog today I had an idea. 

Why not leave the brake lights stuck on and take the 12v switched from the pedal and run it to the brown wire that usually controls the park lights. 

So I cut the brown wire under the cab and all rear lights went out.