The oil pressure gauge will show maximum at all times if:

1) The wiring to the sensor is broken, or disconnected from the sensor.

2) The sensor is defective.

To check for wiring problems, ground the wire to the sensor. The gauge should go to Zero. If it doesn't, then you have a wiring problem.

If the gauge does go to Zero when the wire to the sensor is grounded, then your problem is the oil pressure sensor. Change it

Phil