Rally dash oil pressure gauge issue.

Reads like the sender is for a oil lamp and not a oil gauge. Oil warning lamp sender is either open or closed to turn the lamp on and off. A closed lamp sender can kill a good oil gauge.
Is there a way to tell by looking at it? it looks like my old one, like a bell with a flat male blade tab on it. That may be the issue i put a new sender in when I ovehauled the engine about 13 years ago. I still have the old one, i may throw it in to see what happens.