All,
I recently had an issue with my 1990 IROC Z oil pressure gauge not working correctly. The one in the car would start out at 30 psi and when the engine warmed up would go down to the red area around 10 psi. I hooked up a regular manual pressure gauge and it held a steady 35 psi even when the engine got warm. Obtained two different sensors from AutoZone PS207 and neither showed any pressure at either first startup or right afterward when the engine was running. I did further research and found out the part was supposed to be PS 228. even though Auto zone, OReilly's and Advance stated PS207. Got one of the PS228 from Rock Auto, and it pegged my gauge to the right after running for a few minutes. It also after sitting overnight drained my battery. Installed a new battery because the original was old. Hooked the sensor up again and the same thing happened. Obtained the same part number, same manufacture from Hawks third generation parts and it now works correctly. Just a heads up so to speak. From now on, I will just use Hawk's Third Gen if they stock the part.

 

The oil pressure sending unit is in no way connected to the battery, so something else caused your battery drain.
I got my PS228 from Rock Auto and it works fine.
It is normal to have 55 to 60 psi during warm-up, and should drop to 30 to 45 at operating temperature. Idling in gear (auto trans) should be around 20 to 26...

Is your gauge a 60, or 80 psi?...