Passenger Tail/Brake light out Intermittently

[GregoryJamesQ]

Hello everyone!

So I have owned my current 98 GMC Sierra C1500 for a bit over a year now. Few months back I had each brake light and tail light stop working randomly, which was fixed when I replaced the two rear tail light circuit boards. (Example of part) The problem seamed to go away for 3 or so months until few days ago. My passenger brake+tail+turn light stopped working randomly again, yet the reverse light works just fine. I checked the bulbs, they're fine. I got a electrical tester thing and checked the harness coming out the back that plugs into the tail light assembly, and I did not see power on the passenger side... I did see power coming through on the driver side...

So I checked my Brake Light relay and it seems to be clicking and working just fine... So I replaced my stop light switch (Example part), and the problem continued.

I just noticed now that when plugging in my passenger tail light assembly and my tail lights are on, the reverse lights turn on even when I am in park. But when I unplug the passenger tail light, the reverse lights turn off on both sides... Because they shouldn't be on to begin with....

If you are able to understand my post, does anyone have any idea what could be the possible issues? I am trying my hardest to avoid paying someone to chase wires and diagnose the issue..

 

[Deancr11]

I'd suggest you start chasing wires or thingies which ever makes you happy. I'd also start by cleaning some connection thingies

 

[454cid]

First check your trailer wiring harness and grounds.

 

[GregoryJamesQ]

First check your trailer wiring harness and grounds.

I will check it out after work, and report back. Thank you

 

[GregoryJamesQ]

I'd suggest you start chasing wires or thingies which ever makes you happy. I'd also start by cleaning some connection thingies

I’ll check grounds, harness, and clean connectors and see how it goes from there. I’m trying to avoid wire chasing, but if needed, I’ll do so. I’ll report back soon.

Thank you

 

[fancyTBI]

Brake light issues are common enough that it’s usually 1, 2, or both culprits.
1) the trailer wiring harness adapter near the rear of the frame. It gets full of dirt, which gets wet and turns to mud and compacts over time. Obviously leading to corrosion (no bueno).
2) the ground for the tail light harness that should be on the side of the drivers side frame rail. Mine is attached to the side of the frame. These get weak with age. The terminal can corrode, the frame can corrode, the wire can do the same. At a minimum you should clean the terminal and the frame so it’s back to being shiny metal. You should also put on some dialectic grease to help insulate it from the elements. Inspect the wire. If it feels like a wet noodle (limp, no rigidity) cut off the bad stuff and splice in some new wire. Bigger is better than smaller gauge wire for a ground, but you should try to find similar size.

The entirety of the tail light harness runs from the engine bay to the tail lights along the frame. It should be loomed up.