I have a strange wiring issue with my brake lights. They work fine unless I have the headlights on, then the passenger side light goes dark if I hit the brake. No tail or brake light in other words. I replaced the bulb. Where should I start?

 

I had a similar issue when I first got my truck except both lights were out. In that case, it was my fusebox; a short had melted part of it and messed up the circuitry. Since you've got only one out, that may or may not be your issue. However, still check the wiring from your brakes to your fusebox to make sure there's not anything wrong. If you see any discoloration or abnormalities on the fuse box, it's time for a new one. Easiest way to check wiring is take off the brake lights and look at the color and patter of the wires leading to the fuse box. If I remember correctly, the passenger side light wires go across the rear bumper to the driver's side, go up under the carpeting and along the trim to the fuse box.

See the FSM http://personal.utulsa.edu/~nathan-b...lectrical.html for diagrams and troubleshooting.

 

You have an open ground in your passenger side rear combination light.

Ordinarily, current flows from the battery through the brake light switch through the brake light filament to ground, lighting the brake light. That ground is broken (bad socket, bad wire,...) Now, instead of going to ground, it goes back through the taillight filament, through one of the other rear bulbs to ground. If you remove the bezel you can see that both filaments light when you step on the brake. When you turn on the taillights, that "ground" path is raised to 12v (to turn on the taillights) and neither of the filaments light.

Just pull the bulb holder out of the taillight assembly, and you'll probably find a broken wire to ground (probably white with black).

Good luck!

 

Could be the socket has just got corroded as well causing a poor ground