I bought this 1983 SR5 for $1500. The clutch is worn and the right front axle leaks but the compression is good and no rust. But the TEMP gauge doesn't work. If I short the wire from the sender the gauge doesn't move.
I took the gauge out of the instrument cluster and connected 12v to two of the three connections and the needle went to the top.
What's the problem? New gauge? Bad wires? Sender?
The gauge has three connections but the sender just has one. What is the circuit?
According to the FSM you should have yellow power coming into the gauge, a white black ground and then a yellow-green wire continuing to pass power through onto the temp sender.
How to test the gauge and sender is on pg 677 (BE-27) of the FSM. Sounds like your gauge may be good, and either have a short or a band sending unit.
The senders are pretty reliable, so I would check for grounding or bad wire connection first. I usually have a couple of spare senders around in jars of bolts, so I can swap them out to test them. I did have one go bad once. so it does happen.