Thermostat on Dash is jumpy.

[norcalwood]

I have a 79 300sd turbo. The thermostat gauge on the dash is jumpy. Doesn't tell the true reading. It used to work well. Any Ideas on how to trouble shoot..

Thanks!!

[PatricdeBoer]

Check the connection on the sender. I think it's by the T-stat.

[nhdoc]

This is usually caused by a bad ground in the cluster. A fix is to run a separate ground wire from the chassis directly to the back of the cluster at the gauge, but you can also take the cluster apart and clean all of the connections which make the ground path and probably fix it. These clusters rely upon ground traveling through the metal chassis from segment to segment and if they get loose or dirty they can cause the instruments to jump around.