Temp sensor/gauge problems, 1972 351C

get a multimeter, disconnect the wire going to the sensor.

Put one lead on the sensor where the wire goes, and the other lead on the engine somewhere. You should have continuity but high resistance.

If you get continuity, go from that point on the engine to somewhere on the chassis to check for a good ground.

The circuit will go through the resister in the sensor and ground through the engine. You need to make sure you have a connection from the sensor threads and to ground.

What kind of sealant did you put on the sensor threads? Does your engine have a ground strap from the block to the firewall or somewhere else to the chassis?

Teflon tape can insulate the electrical connection if too much is used. A thread sealant such as SWAK will work better. With that said, I have always used Teflon tape though, no more than 1 wrap around.

You can also ops check the sensor by removing it, and monitor the resistance while its heated.

i'll check my 351 c when I get home. I know its right above the water pump because i was looking at it last night. it sticks out straight towards the front of the car. sooo... I'll check and take a picture of it.