How to figure out bad gauge or bad sending unit?

Grn92LX

Fidanza Man!
Founding Member
Jan 14, 2001
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New York
My autometer electrical oil pressure gauge is reading wrong. I temporarily hooked up a mechanical gauge to verify. Now, how do I test to see if the gauge itself is bad or if its the sending unit?
 
AM can email you instructions to test the sender. I don't know the resistance values or I'd post them.