Crazy/funky gauges alternate resolution.

[HawkDsl]

There are a few threads related to gauges acting up, and or possessed like behavior. 99% of the time, it's related to the "Big Three" ground straps.

(89 moonies cluster/dash)
My issue cropped up like this; I'd turn on the left turn signal, and my temp gauge would max out, and the other gauges would "blink" with the blinker. Replaced the grounds, and it got better, but the issue was still, well, an issue.

And so the hunt begins!

Nearly had the truck completely apart (figuratively), and chasing what I was sure was a ground issue. Sometimes you have to let it sit a few days to let the noggin process it all.

So, truck goes into demon mode with the left turn sig. Followed the wires from the fire wall to the rear lights and found it. The brown wire (hot) 12v supply to the tail lamps had worn insulation, and was making contact with the frame. Didn't blow any fuses, or dimmed the tail lamps at all. Fixed the wire, and replaced all the wire conduit (you know they get crusty, and start to fall apart).

Boom. Fixed.

So, moral of the story is; It's probably the grounds.. but not always.

Hope that helps someone.

(Wire diagram page 119. You can find the diagram here: https://www.gmt400.com/threads/88-98-service-manuals.43575/ )

 

[GrimsterGMC]

Well done, the wiring on these trucks can be a nightmare at times.

 

[LTC_]

Interesting, my 89 does the same thing intermittently. I fixed all the grounds and still same. It tends to do it less frequently on dryer days. Acts up more with humidity (not necessarily rain). I will have to check the harness at the tail lights.