Oil Pressure Gage and Sending Unit Revisited

Thanks guys.
I can certainly measure Voltage differnce between the instrument panel ground and the block.
I can also test the gage operation with the 22 ohm resistor grounded to the block rather than the firewall.

I'm not too hopeful of a ground loop being the issue because the termperature gage also is in hte block, but as you've both said ground loops will do weird thing...

In the meantime I'm coming up with pieces to test the sender from Bill Rolick (short of installing it)