I have been tinkering with this on and off for six months. I can't get my 77 Vega GT, with the 140, temp gauge to read correctly.
Symptoms:
At cold the temp gauge is pegged down where it should be.
As engine warms up it pegs out at 250 and then goes down and steadies out at 210 after about four of five minutes of reading 250.
What I have done:
Replaced sending unit, no change.
Temporarily replaced gauge with a known good one from another Vega I have that reads correctly. No change.
Installed a new grounding strap on the engine.
Checked ground on the instrument cluster (all good).
I have used an IR temp meter and check the actual temp of the engine and it never goes above 194 degrees (even at the sensor area) during the whole time the engine is warming up and the gauge reading 250.
Other problem that may be related to this. My tach reads about 100 rpms high and I notice that it drops slightly when I turn the headlights on or crank up the blower motor.
I am dumbfounded. I followed the wiring diagram and didn't see anything that would cause this problem.
Any help would be greatly appreciated.
Thanks,
Ken