I have an 89 that the oil pressure guage will not show any reading. It is past the 90 psi way to the right. I have changed the sending unit once and never got any type of reading at all on the guage. I have grounded out the wire to the block with no change in the guage.

Any ideas what it coud?

 

i would try the gauge its self

 

I have a new OEM gauge from my old 88 that i never installed.

$35 shipped

 

you either has a Faulty guage or the Wire is shorted to ground some where.......

 

also another thing to consider..... your old sending unit could've been bad yes... but when you bought a new one did they ask you if it was an "idiot light" gauge or a dial gauge???? you couldv'e gotten the wrong sending unit...
when i swapped motors on a previous XJ the donor had an "idiot light" and mine had the dial.... had the same outcome.... oil pressure sending unit showed the gauge all the way to the right....

 

mine went out a couple years ago and the sending unit cost more than a whole new aftermarket gauge so i removed my cigarette lighter since i dont smoke, and used its location to house my new gauge and what was convienent was that the power and ground from the lighter were used for the light on the gauge

 

Thats Awesome! Im gonna have to copy that!