Temp sensor/gauge problems, 1972 351C

[angryman]

The temperature gauge was not working when I bought the car and I later found out the sensor was not hooked up. The wire was laying disconnected not too far away.

I grounded the wire and it sends the gauge to hot so it appears to be working. I replaced the sensor and nothing.
I bought a news sensor and installed it and realized that the stud was too thick and the cap on the end of my wire won't fit on it. The store assured me it was the correct sensor and my internet searches confirm it. I cut off the cap connector and made a direct connection to the sensor stud to see if it will work. Still nothing.

The engine is a 351 C. I am sure I have the right sensor location but just in case, it is on the front passenger side manifold sticking out horizontal just above the water pump.

What the heck do I do now? This is driving me crazy.

 

[j69302]

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.

 

[crankywanker]

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.

 

[angryman]

I used one small wrap of teflon tape one time around and did not overlap. I did find the ground strap connecting the top of the manifold to the interior engine bay near the battery.
I'm not very understanding of electrical aspects and troubleshooting but I'll get a multimeter and do what you said.
Thanks