oil pressure gauge problem

[RuralRoute C-30]

(Originally posted in the wrong forum)

So the '85' C-30 got front and rear seals replaced along with the oil pan gasket and timing chain(old one was loose) and cover, and now, the oil gauge reads as if the motor was on when its not. Even when the ignition is on it doesn't move. Coincidence or maybe a bad sending unit appeared? Was a ground I didn't notice get touched in the process?

No leaks around the sending unit.

Is there a way to test to see if it is the gauge or the sending unit? Dare I ground the wire from the sending unit and expect what, if anything to change? It is a one wire sending unit.

Beats me how one fix leads to another, and nothing near the sending unit was touched, but hey, it is an old truck and I am an old man which makes me quite familar with getting fixed in time for something else to break down!

Any suggestions is appreciated as "I do not know", bad sending unit, ground, gauge?.
Thanks,
Mark