Strange temperature gauge issue

79 Dodge D150, 360 CI

Temperature gauge works fine, that is until you turn the lights on. Then the gauge will climb, some times it will peg others times it it goes to three quarters. Now for even more strange, when you turn the dimmer switch up, you can watch the gauge climb, turn it down the gauge will drop. Turn the lights off the gauge works normal. Truck is not over heating. I believe it is a faulty dimmer switch, but it turn the lights off and on fine and controls the dash lights.

Has anyone run into this issue? potential causes and fixes???

Its a ground issue, been there done that.

Ground to what GJ! in the dimmer switch it self, or the temp gauge? They both work.

Cluster to dash that grounds through the screws holding it in?

It could be any multitude of places. As these trucks age contact points between body panels get corroded and lose continuity, ground points themselves do the same. It's time to find and clean to bare metal every ground point on the truck. If that doesn't fix it then running new ground wires from body panels to the frame or directly to the battery is the next step.

Thanks guys! I guess I have some investigation to do.

I installed a set of Cyberdyne aftermarket gauges in my 70 when it was built...no issues until a few years later when I installed the stereo system...

When the volume was turned up the water temp would peg and the oil pressure would drop...

A ground wire from the gauges ran to the engine and not just the dash frame cured the problem...

Sounds like your IVR is acting up. If you think it is a ground problem, a lot of the later IVR's have a tab on the case that does is not connected to anything. I'd run a test wire from this tab to a good gorund and see if it makes a difference.

IVR

grounds are funny things. can't have too many of them, and the connecting points must be clean and tight.
they can also cause hair loss on the top of ones head from chasing them to find the one that is causing the problem[s] you are having. i have no hair on the top of my head.

Dial-a-temp ! Who knew ?

Sounds like it's time to pull the cluster & clean up whatever's creating the feedback.
Might as well look at the bulkhead connections and grounds, too.

Yes, chasing electoral issues will leave a man bald!

It is pretty strange to watch, I will have to take a video of it!

Yea, I see some work in my future!

If you can establish a grounding point on the printed circuit film ( usually under one of more screws) running a wire from one of thes points to the dash frame is a quick fix. most of the time tightening the screws (cluster mounting included) will do the trick

As I recall that dash has a ground wire. Look at the dimmer switch for a ground wire that should be on one of the screws. I think it is white in color. A FSM will show it. I know for sure the 77 had it and I think it stayed that way through 1980.

Thanks for the "Tip"

All right, an update after some investigation.

I pulled the instrument cluster and cleaned all the contact points that I could access, I found one burned out bulb, emergency brake light. I also checked the bulkhead connector, it was tight with no loose wires.
The issues was better, but still there. As I was putting the ground back on the battery, I told myself to check all the ground to vehicle connection, the very first one was battery to engine. At first it look good, but I decided to pull it off and clean the surfaces. Upon loosing the bolt just a little, the cable fell off. The end connector was broken in two places. I put a new end connector on. I found one other body ground from body to transmission with a bad end as well. Cleaned all other grounds I could find, I fixed a bunch of wiring connections from previous owners, trailer brakes (wired with Romex wire), stereo and trailer plug that were only held together with twist ends and electrical tape!

For now the issues has gone away and the seat belt indicator buzzer has decide to work, but will probably get unplugged soon.

Thanks for all the help!

See I told ya!

thanks for the update

how much hair did you loose from the top of your head finding these culprits ?
glad to hear you have had success in repairing your issues.