Onan Generator Fault Code 2- Low oil pressure

Starting about a year ago my 7.5 KW diesel generator on about every 3rd start attempt would start and run for about 5 seconds and then auto shutdown flashing a low oil pressure code. This only happened about a third of the time and only on start up. Once started if it didn't shutdown after 5 seconds it ran normally. It never shut down after a successful start. I changed the oil and filter and topped the oil right up to the top of the oil dip stick. This worked for about 6 months and then started again. I over filled the oil by about half a quart and again that seemed to fix it for about a month or about 10 start attempts before it happened again.

Now it happens about half the time. It starts and runs for about 5 sec and displays 2 flashes on the start switch indicating a low oil pressure issue. But again when it does start successfully it never auto shuts down, ie it runs until I manually shut it down. So it is an intermittent issue.

It is impossible to get to the oil pressure sending unit without virtually taking the entire engine apart. I would like to verify the engine is getting oil pressure. I can get to the white wire leading to the pressure switch and am wondering if I can verify oil pressure in some way by testing the wire to the oil pressure switch.

Any help is greatly appreciated. I've been chasing this problem for almost a year.