Hello FTE,
I am having some issues with all of my rear lights. The 3rd brake light seems to be okay, but the others are not. Originally I believed it to be a grounding issue, but after adding a ground to the passenger side brake light harness, my issue still remains. From what I understand, there are two bulbs in each of the rear tail lights. One of these bulbs is for reverse, and has only 1 filament. The other bulb is for everything else, and has two filaments. One of the filaments is for the running lights, while the other is for braking and signaling. My issue is that all 3 of the functions (running lights, signaling, and braking) are all going through the same filament, while none are going through the other. The lights are also very dim. On top of this, when I put the vehicle into reverse, the reverse bulbs do not light up whatsoever. Any help or suggestions would be great, as tomorrow I am going to continue troubleshooting but will likely have to trace the entire harness which I do not want to do. The truck is a 2004 Ford Excursion 6.0L PSD. It was just sandblasted and repainted underneath, but I haven't seen any issues or noticeable crimps/cuts in the harness running along the chassis. I have also cleaned the connectors. I have also recently replaced the flasher relay, because my 4 ways were acting up.

 

Really need some info, guys. Someone please offer some insight, I'm thinking the turn signal switch is a possible culprit since the 3rd brake light is working just fine?

 

Sounds like something you'll need to dig into and visually check. You never mentioned if the issue was present prior to sandblasting. Try removing and unplugging the trailer socket connector to see if the problem is still there, remove the rear bumper if needed to inspect all tail wiring leaving the Pass rear quarter area (behind the right taillight possibly) from the rear Aux climate component area and connecting to the final bumper harness.
There are wiring diagrams in the Tech folder, one diagram is for tail lights, albeit 99-01, the wire colors will be different, but the circuitry may be identical.

 

Thanks for the reply, it ended up being a grounding issue. Spliced in a new one and all good to go, very happy I can put this behind me. Will post the electrical diagrams tomorrow for anyone that has this issue in the future, they were very helpful.

 

Not sure if you had issues with the instrument panel as well but I am having issues with my rear running lights, fog lights, instrument panel all not working and blowing a fuse. Any help is appreciated

 

That sounds like you have a dead short somewhere. Check the wiring around the E Brake pedal for any wiring damage.

Instrument panel work before you turn on other lights?