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Old 06-30-2012, 09:54 PM
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dash loom ground wires for gauges are hot

We took out dash of 75 Trans Am to recover and are now re-installing the dash.

The ground wires in the dash loom are hot in the ignition switch run position and all the gauges move to the let when the switch is on.

The clock in the instrument panel runs when the ign switch is in the off position and stops when the ign switch is in the run position.

We took the fuse block apart while the dash was offf and put it together and now we have these issues.

Don't know where the ground wires start from that are in the dash wiring loom either. Anyone know this??

Can anyone give me some guidance on how to trouble shoot this.
Thanks

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Old 07-01-2012, 06:31 AM
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There are few things it could be.
I suspect you have a missing ground somewhere
A direct short would blow a fuse.
Does that have a printed circuit on the cluster? A printed circuit can be brittle and an open ground in a circuit is common.To fix it sometimes you can jump a piece of wire to bridge the open circuit. Just Please be sure what you are jumping before you do.
You can check a ground path easily, just hook the test light to the positive side of any source, and follow the ground path on the board, from point to point where it connects. No light means you have found the culprit.
I would look the printed circuit over real good first, it may reveal the problem with a close look.
The plastic gets old and brittle, and cracks, then the copper strips, split making an open circuit.
I would check the grounding point of the ground wires in the dash loom first. It sounds more like a ground wire not connected to the firewall at some point.
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Old 07-01-2012, 07:57 AM
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Moving this to Electrical.

Dan
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Old 07-01-2012, 08:11 AM
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we bought a new printed laminate circuit for the speedo and tach and you can see a light brown area that got hot but it ohms out between this 1" area.


there is a small black wire that is on the L.H/ side of the dash that goes down
and connects to the drivers door switch that has an additional black small wire with a small ground lug with the metal serations that READS 12 volts WHEN READING THE FLUKE VOLT METER. I DIDN'T CONNECT THIS TO GROUND BECAUSE I WAS AFRAID OF SHORTING SOMETHING OUT. IT WAS TWISTED TOGETHER WITH ANOTHER LARGER LUG GROUND THAT DID NOT DISPLAY 12 VOLTS WHEN GROUNDED. This has a large bolt hole for like a 1/4" bolt that I HAVEN'T ATTACHED THE THE DASH FRAME AND LIKE I MENTIONED IT DOES NOT DISPLAY 12 VOLTS WHERE THE SMALL ONE DOES. BOTH WERE CONNECTED TOGETHER THOUGH. SOUNDS LIKE I NEED TO ATTACH BOTH TOGETHER TO THE DASH STRUCTURE EVEN THOUGH THE SMALLER ONE HAS 12 VOLTS BEING READ, RIGHT??????

other interesting points are:
the high beam indicator on the dash is now on the low beams and off for the high beams.

all guages including the tach move to the left when the key is in the run position like the power is reversed. Will disconnecting the connection at the instrument cluster where the printed laminate board is be a good step in isolating this? There is an instrument light off the cluster that has a long pig tail that is attached to the ash tray housing for a ground.

where are the ground wires attached to the body or ??? that are part of the loom coming from around the fuse block??

WE DID take the fuse block apart and put it together to check it out too.

It seems that every circuit is backward except for the one going to the cigarette lighter, 12 volt on hot and nothing on ground?

This electrical stuff is challenging for a 71 yr old hot rodder but it will be good learning experience for my 16 yr old grandson as this car will be around for a long time.

Hopefully this give more food for thought until I start back on it in the garage.

thanks for everything and I'll be back when I check things out.
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Old 07-01-2012, 08:30 AM
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Another couple items to mention,

I found that one of the fusible like wires this coming off the alternator's large 10 ga wire ( It splits into 2 wires with 2 fusible links) was barely attached. I pulled it apart and bared the end and for now have it attached to the lug where it splits into to wires secured by small vise grips. CAN RE - USE IT BY CUTTING ON THE 10 GA WIRE AND CRIMPING IT WITH A BUTT CONNECTOR THERE???? I got into this loom when I replaced the starter solenoid wire with a larger more robust wire because the 400 engine has headers

Also, along with the prior post. when I turn the ignition key to the start position, I don't get 12 volts when checking the solenoid wire to ground of the engine. Is this related to the suspected ground problem above????
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Old 07-01-2012, 08:47 AM
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Quote:
Originally Posted by DanTwoLakes View Post
Moving this to Electrical.

Dan
Thanks Dan
This is the one site that has members that really stay on helping
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