How do you test the temp. sender (to the gauge) and/or the gauge itself ?
When I bought the car the temp gauge was broken, so I installed a mechanical gauge (never found the origanal wire to the sender (between 1 and 3), then I installed a new gage cluster with seems to be a good gauge, after buying the new sender for the car (which didn't work- threads too small) I realized P.O. installed different heads.
Found correct sender for that head, removed the green wire (2 into 1) from the C100 connector inside the car and ran wire to the sender, but still the same thing, gauge at bottom reading until cranking the engine at which time gauge pegs max until stop cranking and justs sits at bottom? Previously removed AC, ECM, ALC, and anything else I didn't need if thats any help. Gauge max's out when grounded, so it must be a wrong sender.

 

You can test your temp switch for resistance and certain temps to see if its good. If when its unplugged your gauge should peg cold. If you plug it in and it pegs hot then its probably a bad switch. If it pegs hot when not plugged in you have a short along the green wire or your gauge is bad.

Ohms @ deg. F
13500 @ 20
7500 @ 40
3400 @ 70
1800 @ 100
450 @ 160
185 @ 210

All are approx. It should be pretty close to these values but does not have to be exact.

 

yea sounds like the sender is open or of to high resistance.