1989 GMC C1500 Dash gauges, turn signals and lighting

JAMMER74

MEMBER
1989 GMC C1500
V8
2WD
AUTOMATIC
190,852 MILES

When I turn the headlights on, my dash gauges all move to the far left, and when I use the turn signals, all the dash lights, gauges, indicators, ect flash in rhythm with the turn signals. It really sounds like a ground problem, and I have repaired and resecured all grounds that I knew where to look for, ie. The main body ground from battery and the ground cluster that attaches to the thermostat housing.I am a master ase certified technician, but I am in between jobs right now, as my Dad just passed away, and the shop he owned was sold to provide for my mother.I was working for him, but I haven't found another job yet. And without a shop I have no access to informational sources. So any help would be appreciated.

3 Replies

DR LOOT

MECHANIC
2,311 POSTS

The thermostat housing is not a very good main ground, the main ground should be grounded to the frame, and from the frame to the engine block, or the head, not the thermostat housing, also make sure that your body ground is connected to the fender, Next to the battery that is critical for your cluster and all other body Electrical components.

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Wednesday, October 28th, 2009 AT 11:43 PM

AREA52

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8 POSTS

Did you ever find out what was wrong? I have the exact same problem on my 89 GMC C1500 SLE. Turn on the signal lights & all the gauges go to flopping in sequence with the flashers. Turn on the headlights & all the gauges max out to the left?
Let me know if you ever figured it out. Maybe it'll save me some time searching & running wires for shorts & grounds.

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Wednesday, April 25th, 2012 AT 7:32 AM

NETCENTS

MEMBER
1 POST

I have the exact same issue and found this at another site. May be helpful to others visiting with same issue at a later date: ALSO many are saying the ground from the negative battery cable to the fender and from the frame to the engine block can affect guages.

Hello and thank you for using JustAnswer. My name is XXXXX XXXXX X will do my best to help you with your GMC problem.

The problem is a bad ground. The lighting circuit is not getting a good ground so it tries to pull a ground through the gauges and signal lamps. Try running a new ground wire from a good ground source under the dash to the black wire at the instrument gauge cluster connector. Make sure the connector is good and no terminals are bent.

If this does not fix the problem, then you have a break in the circuit board for the gauge cluster.

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Friday, June 22nd, 2012 AT 3:23 PM