Guys on one of my engines I get an occasional warning beep/alarm that comes and goes for no apparent reason. I get the normal two beeps when firing up and have checked for any faults/codes
after getting the alarm and it says general fault but doesn't identify from where. When the alarm goes off there is no change in temp, oil pressure, etc. and I've checked the drive reservoir which is fine.
Oh and when the alarm goes off there is no noticeable change in performance either. Thinking something must be grounding out somewhere to cause the alarm. Even thought about swapping the
ECM's to see if the problem follows it. Any other suggestions/thoughts?

unplugg the single wire to oil press safety switch, see if it goes away then unplugg wire to drive lube resoivoir, with wires unplugged defeats the ground circuit that causes the code, if one of those does it, theres your answer.

Adding to what arctic friends posted above
And also unplug the high water temp alarm sensor. All the alarm wires are tan with a blue stripe.

These 3 things are the only things that set off an alarm on a MEFI 3 and there is no guardian mode.

Also, the gauges use separate sensors from the alarm system

Thanks guys...I will try that. I wasn't certain how many sensors were tied to the alarm system.

So I am trying to eliminate the three sensors being the issue by unplugging them as suggested. Disconnected the drive oil sensor and made no difference. Was looking for the coolant temp sensor and oil pressure switch (not the sending unit) and the engine was too hot to really look for them. Disconnected a single wire below my oil filter but that was for oil temp. Been trying searches to figure out where on the block they are located but haven't found anything so far. I think I found what I think are pics of the coolant temp switch and low oil pressure switch on marineengine.com but not sure. Would you guys happen to know where on the block these two switches are? TIA

The oil pressure switch and sender are located on the block near the oil thermostat, right rear side of engine.

Water temp alarm sender is near thermostat housing

Also, if the alarm still sounds after disconnecting them, the tan/blue stripe wire has probably rubbed through somewhere and is grounding out

Don't the 500 EFI's use the engine coolant temp sensor and the MEFI3 outputs the high temp alarm? My manual shows Oil Pressure and Low Drive Oil the only two alarm switches, I think the rest of the alarms come from the MEFI.