I have a 1990 E-150 4.9. The temp gauge and the gas gauge randomly read really high then drop. The temp is fine, the gauge will jump to almost "H" then come down. Same with the gas gauge. I've traced wires but no luck so far. Any guesses?

 

I wouldn't want to guess wrong , so I will suggest something that might help.

The instrument cluster is not that difficult to pull back, the only thing you need to make sure of is, that the speedo cable is not anchored down where it could prevent you from pulling the dash out far enough to do as I will suggest. That way you don't have to disconnect the cable..With the dash out some , you might unplug one of the wires to the fuel gauge, then turn the key on and see what you get .If it behaves normally , the problem is in the fuel gauge or wiring.If no difference,then the problem is with the temp gauge/wiring. If I recall correctly the temp gauge supplied the reduced voltage for all the other gauges to operate. All you are attempting to do is isolate the problem area.. Let us know how you make out with this, thanks.

 

Hey it gives me a solid place to start. I've replaced the gauges and the sending unit and still the same issue. I'll see if that helps

 

I had the same problem. It was a bad ground for the instrument cluster.

 

Oh cool, I"ll try to track that down. Thanks for the heads up