Thanks alot guys for the help, I really appreciate it!
The Autometer ground wire grounds via the gauge black wire. That wire should go to a GOOD solidly connected body shell ground connection.
Yes, I have several of the gauges grounded together to a 12 gauge wire and routed to a grounding bus bar at the driver's side kick panel area. I know you said resistance without power is meaningless, but I measured the resistance of only the bare connector to the bus bar and it's 0.3 ohms.
If you want to check the gauge ground with the key on and power applied, you have to measure VOLTAGE from the ground pin to the vehicle chassis. Any voltage over a small fraction of a volt indicates a ground problem.
When I measured the back of the powered gauge (I had to use paperclips to access the connectors rear terminals), there was no voltage to ground for neither the gauge ground nor the sensor ground. Oddly, I noticed that if I touched the paperclip, there was a slight voltage - around 0.17V.
You could have a bad sensor. Measure the ground pin resistance to the sensor shell without any power and nothing else plugged in. Just the sensor itself.
There is no resistance/continuity between either of the 3 pins to the shell, when the sensor is sitting my hand with nothing connected.
Does the needle auto calibrate on every power up?
Yes, the needle makes a full sweep and then goes directly to 0.
Is there a way to test the gauge like the short sweeps by grounding the signal wire and seeing if the gauge maxes out?
Also what did Autometer say on how to test?
When I hold the sensor in my hand (connected), I can pressurize the gauge with my air compressor and the gauge responds fine. Holding pressure steady and just touching the shell to an engine bracket (ground), the gauge immediately goes to 0. - strange.
Autometer just wants me to send everything in.