Third brake light wiring question

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df2x4

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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?

IIRC the cargo lights should come on when a door is open, as long as the cargo light switch on the dash is turned on.
 

Martin Evans

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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
I believe that your bottom left white wire is a ground also. I'm not certain for the '97's though. I have an '89 that I added the 3rd brake light/cargo light, so I had to add new wiring. I just tapped into the dome light for the cargo light instead of running a separate wire to a switch. For the brake light, I ran a wire to the stop light switch and grounded it with the dome light attachment screw.
 

Martin Evans

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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
That should work.
 
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