My Windsor
oil pressure (Autometer gauges) goes up to ~50# when first started, and the
oil is cold. When the engine warms up,
oil pressure runs ~20# - 25# at idle, then goes back to ~50# cruising/highway.
The suggestion made to check all grounds is a good one. You have to have metal to metal contact on the threads on at least part of your sending unit or you won't complete the ground. Same for the block to frame to battery ground. Don't use teflon tape for automotive use. Use teflon compound out of a tube, and only for water. In fact, Locktite blue, or plain old Permatex will work fine. Do a trial assembly, then apply sealant to the upper half of the threads to get metal to metal contact, and a good electrical ground on the bottom half.
Another way to test things is on the bench before you put it in the car. Hook it all up with a battery charger and alligator clip leads.
The thing we "Assume" is going to work, even brand new, DOESN'T! The assumption I made was that my fuel tank sender would work as advertized. Hah, Murphy strikes again! Second time, it all got bench tested before installing.