I've put a tacho dash into my exec along with a oil pressure sender which i got from my wrecked VL. I've plugged in the taped up blue wire, but my oil pressure guage still flys right across to the right, even when i un plug it it stay to the far right. How do i get the guage working?

Ive done the same thing, some people here have suggested that a Calais wiring loom transplant is also needed.

Only the upper loom .. I swapped mine when i did my dash and sender conversion, and its worked fine. I'd heard it wasnt needed to be done, but might be needed.