My 36 MK 1 with the Universal M25 XP has just begun to sound the alarm at the switch panel when the engine is running. There is no oil pressure gauge at the panel, and no oil pressure idiot light. Since the coolant temperature is normal, I am assuming that this alarm is from the oil pressure circuit. The engine oil level is at full, and the engine sounds and runs normally. I disconnected the blue wire to the oil pressure switch in the block with no effect. Today I replaced the oil pressure alarm switch, again with no effect. I read on the forum that a failed resistor can cause this, but that resistor was apparently added to the circuit 10 years after my boat was built. 
Any thoughts on what is causing this, and where to go from here? Thanks