Temp gauge issue

[ScottH]

Truck is a 66 c10 with factory gauges (not idiot lights) with original 327 engine. When nothing is turned on the temp gauge reads almost on H, pointer is just at end of green line. When ignition is turn on the needle jumps right to the C. When running the needle never moves.

If I ground the sender wire, the needle jumps past the H.

I'm guessing the sending unit needs to be replaced, but wasn't sure if the action of the needle would be correct if this is the case.

Any info is appreciated.

Thanks