Temp. Gauge Input?

[alta-aj]

I have a 79 400 in my 72 Jimmy. Ever since I installed it, the temp gauge hasn't worked. In fact, I'm not even sure if it worked before the engine changeout occurred.

I took the sender out today and put a flame to it and the resistance decreased from about 3.4K ohms at about 65 deg. as the temp increased. So, seeing I had responsiveness from the sender, I hooked the (dark green) wire from under the hood back up, made sure the sender was grounded, applied the heat again and still, no response at the gauge.

Can anyone tell me what the input to our vintage temp guage is (in case the 79 sender is incompatible) and what the range of the input is?

Any other suggestions as to what may be wrong?

Thanks for the help.