Have an 1988 F150 with the 300 six. The temp guage is pegged and the red engine light on the dash stays on, the truck does not appear to be running hot and the check engine light is not on. I understand there are two temp sensors on this rig. This happend to the truck about seven years ago and the dealer hit me for both sensors and a new guage, Pretty Spendy. Any suggestions. I had the battery disconnected for a few days as I just put in a new clutch.

 

You might have pinched the sender wire and grounded it agianst the engine. I would find the sender( one is for the computer, the other is for the gauge) and follow the sender wire looking for a ground. if you find the sender( should be the one with 1 wire not two) and you unplug it it should turn off the light and put the gauge back to 0. If not, you diff. have a wire prob.