weird gas gauge problem

My gas gauge reads empty when full and full when empty!!!!

I swapped tanks from a '95 into my '90. The electrical connector only plugs in one way. I'm guessing that the wiring is different for these two tanks. Is my only fix to swap pumps so that the electrical is the same? Or can I fix the existing wiring so that my gauge reads correctly? The pump on the '90 tank was really noisy, this one on the '95 runs nice and quiet.

Pop the pins out of one connector and reverse them..

thanks for the idea, rich! now why didn't I think of that???