99 tahoe electrical gremlins

Picked up a 99 hoe on a trade. Kid having issues with it running right. Runs like total shit no power tries to die. I was curious since he installed the deck recently if the plug behind the glove box had anything done with it for the rear speakers to work if I remember correctly, sunlit helped me years ago with this but I can't remember what exactly I did to get rear speakers working.

Funny thing is when I unplug the harness behind glove box it runs perfectly. Has power like it should. But my cluster has no power. Plug it back in runs like total shit again. All the 4wd lights stay lit up and neural light. Turn key off power cuts to everything. 4wd doesn't engage. Kinda lost where to start here. Any help much appreciated

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please. If we can't see it, it does not exist.

I cannot personally assist you with your issue, but other members of this Forum much more knowledgeable than me in your truck will chime in.

How did it run before anyone working on it? If it was OK then undo the human intervention whatever that was.

that99hoemama4 said:

Picked up a 99 hoe on a trade. Kid having issues with it running right. Runs like total shit no power tries to die. I was curious since he installed the deck recently if the plug behind the glove box had anything done with it for the rear speakers to work if I remember correctly, sunlit helped me years ago with this but I can't remember what exactly I did to get rear speakers working.

Funny thing is when I unplug the harness behind glove box it runs perfectly. Has power like it should. But my cluster has no power. Plug it back in runs like total shit again. All the 4wd lights stay lit up and neural light. Turn key off power cuts to everything. 4wd doesn't engage. Kinda lost where to start here. Any help much appreciated View attachment 486709

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I had a 1999 Tahoe SLT 5.7L before I purchased my 2012 Yukon SLE. The 1999 had electrical problems like the rear wiper and the drivers door console worked intermittently. The problem was the OEM connections were weak. After I resoldered them they worked fine.

The connections from the factory were really brittle and any movement would loosen or break them. I had to be extremely careful when working on the electrical system. I had it from 1999 to 2014 so I would suspect your electrical is far more fragile now than mine was in 2014.

You can try checking the resistance of each wire to see if any shorts or issues have developed. Inspect the wiring for breaks. Inspect the connector and pins for issues. Ect.

You can also use charm.li to determine what harness that is, what it does, and where its goes.

The connector behind the glovebox should be C200, but check the wire colors to see if it matches:




Glancing through the circuits, it’s largely transmission mounted controls but I see one circuit for the brake switch. It’d be worth checking the wiring on that - does the gear indicator show the correct position? The lights on the 4x4 switch could point to the transfer case control module (driver side dash) or suspect wiring going to it.



As mentioned earlier, undoing any “human intervention” in the wiring is probably the first step. JoeBlobs linked the factory manuals above, they have the diagnostic procedures for any codes and symptoms.