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1999 gmc Sonoma electrical issue

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New User

Feb 19, 2020, 7:11 AM

Post #1 of 3 (337 views)
1999 gmc Sonoma electrical issue Sign In

Hello all, new guy here. I recently bought a 1999 gmc Sonoma. To make a long story short it had been sitting for 8 or 9 years due to a city trading it in to a dealership (it was a meter reader pickup in Tennessee). The dealer sold it at auction and it ended up in Sherman, TX and my friend who has a landscaping company took it in trade for a job with the dealer in Sherman, TX who bought it. I bought it from my friend via FB Marketplace for $1,800 with only 89k miles. The truck starts and purrs like a kitten but has the following electrical issues which may be related.

None of the 4 turn signals work
Brake nor rear parking lights work (no lights at rear work) Truck thinks that the drivers door is open (when key is out and you turn the headlights on it dings)
Flashers don't work but the relay under passenger dashboard buzzes
Fuel gauge bounces from full to empty (low fuel light goes on and off) (guage most of stays on empty)

I think those are all.

Any replies are appreciated and


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Feb 19, 2020, 7:30 AM

Post #2 of 3 (333 views)
Re: 1999 gmc Sonoma electrical issue Sign In

! It's totally been way overexposed to up to 9 years of just sitting? Fine but expect near endless problems like that it's gone thru all those cycles of damp to dry inside and out every last electrical connection and ground exposed.

One by one pull flashers, connectors anywhere, grounds to frame, frame to body all thru it. If pick-up bed that too must be grounded so does trans and find out back rear differential probably to frame.

Inside the lenses may have circuit board like things for bulb stressed out flashers, headlight switch and wiring - this list goes on forever.

Try away if it's been another while since anyone really used it and put some miles on it expect leaks next the shafts sealing about anything had to have dried up and at least gun rusted will tear and leak.

Could be a great buy for you if the time or for good body parts for another I question interior mold issues hope that's not also in the mix.

If you didn't expect a total project you really shouldn't have taken on anything with that history IMO,


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Feb 19, 2020, 7:46 AM

Post #3 of 3 (330 views)
Re: 1999 gmc Sonoma electrical issue Sign In

Electrical problems are not solved on forums.

You tackle one circuit at a time using a wiring diagram. When you resolve one issue, you step back and see what issues you still have and the attack the next circuit that has a problem in the same way. If one solution corrects more than one problem, that is a bonus.


We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.

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