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Check that K20 (Oil pressure fault relay) is engaging when starting up. You can view the internal relay arm moving when it starts up. The MEP803 I worked on last did not engage. Had corroded contacts preventing K20 from energizing. If K20 is not engaged, it will not see the LOP fault.

No, there is a lot going on in that circuit and with no oil pressure, the LOP switch is effectively shorted as it using the N.C. connection. You need the motor running. As long as your motor is making oil pressure as indicated on the OP indicator, you are not going to harm anything by running...

The LOP circuit allows the motor to run when it is open or disconnected. That's why it connects to N.C. and not the N.O. contact. When the oil pressure comes up above 15 lbs. or so, the LOP switch opens. To test the fault circuit connect (short) the two wires going to the LOP and it should...