Third brake light wiring question

[robnb2]

So I'm new here and have a 1997 sierra sle 1500 with a quick question about the wiring for the 3rd brake light. My third brake light doesn't always work and I figured I would surprise my inspection guy this year with it working. Since I had today off I did some testing and got the brake lights to work and the cargo lights to work with the switch. I am missing power on 1 white wire. I thought it was a courtsey light but not 100% sure (the lights on the door and dome light come on when I open the door).

4 wire connector
- Top left white wire - 12 volts when pushing on brake pedal.
- Top blue/white wire - 12 volts when cargo lamp switch is on
- bottom left white - no voltage
- bottom right black - ground

 

[GoToGuy]

Did you look at the wiring diagram? The factory service manuals are free to download in this forum. Has all electric.

 

[chevyrider838]

Same issue for me, bought a cheap assembly from Amazon, hard wired it and nothing. Bought an Anzo third brake light because the reviews said it was plug-n-play and still not working.

 

[GoToGuy]

Did you refer to the wiring diagrams for your year truck.

 

[chevyrider838]

Did you refer to the wiring diagrams for your year truck.

Yes I did…also did some testing on the 4 3rd brake light assembly wires this evening and discovered that my ground wire is bad. I just replaced the rear pillar 4x6 speakers and re-did the headliner while I had those panels off….could’ve fixed it then had I known…really not wanting to pull any of those pieces off again. It’s a miracle nothing broke…next time might not be so lucky lol.
Wondering now if the metal right behind the light assembly would be a good ground….any suggestions? Thanks

 

[GoToGuy]

If you can find an area that won't interfere with reinstalling the assembly, and functionally tested it. Then sure, and if there is ever a problem again, your troubleshooting will be a little easier. Good luck.
I installed an LED assembly on my 95 K2500 two years ago, and have been very happy with it.

 

[chevyrider838]

If you can find an area that won't interfere with reinstalling the assembly, and functionally tested it. Then sure, and if there is ever a problem again, your troubleshooting will be a little easier. Good luck.
I installed an LED assembly on my 95 K2500 two years ago, and have been very happy with it.

Ok thanks...I'll let you know how it works out.

 

[AuroraGirl]

Same issue for me, bought a cheap assembly from Amazon, hard wired it and nothing. Bought an Anzo third brake light because the reviews said it was plug-n-play and still not working.

check your wiring from the cruise control system and also the exteriorr lamps diagrams. ive seen the signal be sent from,to, and mutually from brake switch etc. idk what trucks do. id imagine if there is a third brake with cargo, its related to its own dedicated line (To be separate from tail and that, and it prob goes 2 places.)

 

[GoToGuy]

As the wiring diagram shows the third is powered before the signal continues through the rest of circuit turn and stop circuit.

 

[chevyrider838]

UPDATE: I used a self drilling screw and created a new ground from the small metal hump behind 3rd brake light assembly. Wa-la…that fixed the grounding issue but the Anzo light still won’t function properly…I’m thinking wires in the harness don’t match up and pretty sure if I cut connector and hard wire, it would fix that issue. I’ve decided to use an OEM assembly I found at a local salvage yard in great condition and use spray tint for the smoked effect on the lens. All lights work in OEM assembly but cargo only turns on when dimmer wheel is all the way up….is that standard or does cargo light supposed to turn on when door is opened? Thx!