98 Jimmy electrical problem

1998 GMC Jimmy it has auto head lights. My problem is intermittent, sometimes I loose power to the heater, radio, interment panel (speed, tach, warning lights, fuel, etc) power outlets, but the car still
runs. If I manually turn on head lights I hear a clicking sound under mid dash area. Then everything starts working.
I thought maybe it was the wiring harness from the firewall up the steering column but that did not fix it. I then cleaned the ground wire from the battery to the engine but still have the problem.
Today I ran a new ground wire from the firewall to the engine and it seems OK. Then a test drive and I hit a bump and off the power went. It must be a connection from the fire wall to the interior but I dont now where to look.
Any ideas of what to look for would be appreciated.
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You need a factory wiring diagram which would be in a GM factory service manual set (order from helminc.com). Then a multimeter.
Then when the problem occurs, trace the problem in the wiring using the multimeter.
If you don't know how to read wiring diagrams or how to use a multimeter, might take your vehicle to a GM dealer, however...
...automotive types are not very skilled in the electrical area. Especially "intermittent" electrical problems! So you might be better off taking a few months to learn how to do this yourself.
You might take it to the dealer, the problem does not present itself, then they say they can't find any problems! You however would have the time to track down the problem.
So learn all about multimeters. Learn how to measure things and what the different setting are for.
Then get a book on basic automotive wiring... (Something like this...) http://www.tracyamartin.com/WebPages/Autobook1.html
Read the book cover to cover.
"tim" wrote in message

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Ground connection on the back of the dash. The harness has a couple of connections and each has it's own ground path. You may also want to look at the junction block at the firewall where the main harness connects to the interior harness. There have been a few cases of the pins getting corroded and causing intermittent problems.
The easy way to tell would be to give the dash a good smack when the power drops. If it comes right back the problem is likely the ground for the panel. It's a PIA to access without pulling the dash (which actually isn't that hard, just time consuming). Also try reaching down and giving the harness connection on the firewall a nudge.
Another place to look would be the main power feed for the interior.
--
Steve W.

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