Hello all! I’m finishing up the interior on my Vette and I’m having some issues with the gauges reading incorrectly. My oil pressure gauge and tach have been giving me a headache. 

the tach has a new Wilcox board I bought a 2 years ago. It has been zero’d however when the engine starts the needle gets stuck between 3500 and 4000 I believe it to be a grounding issue with the plug. 

next issue is the oil pressure gauge, I have tested it by grounding and it goes to zero, when the circuit it’s open it pegs at 80. However when the engine is running it pegs at 80. I’ve tried two sending units both of them do different things. 
1st one, key on 0 psi then when running it pegs at 80

2nd one key on 40psi, running it will jump up a bit like it’s actually working but a bit short of the 50 psi when the oil is cold. 

confirmed my hot idle oil pressure with a mechanical gauge at 35 psi, and 50 cold. 

could this possibly be the resistor on the gauge? If so can I pull the resistor off another gauge and use this to test it? 

I would imagine there is a valid resistance check for the oil sender. I would start there before tearing into any more parts. It worked when new so what has been changed?

The Tach maybe a stuck needle in the gauge itself, or wrong electronic components for the 77.