Ok, read through and 'up to speed'. I concur with
muc. There are 2 oil pressure senders/sensors on the engine. One (the one with a single lt blue wire) is for the analogue gauge and the other (with 3 wires, grey, black/pink and dk blue/yellow) are the voltage divider type sensor for the ECU. And yes, the alarm is controlled by the ECU, based on what the voltage divider sensor is reporting.
If you changed both fuel and oil filters, then I agree, you have air in the lines, pretty much guaranteed. With the oil pressure I also agree with a few of the suggests here, just start it up with plenty of water on the hose and give it 1500rpm. With no load on the engine, it would probably run for quite a few minutes before damage. You COULD prime the line by removing the filter and filling the supply line with oil. That would help it out. The supply line for the filter (the one running back to the pump) is the outer one, not the centre..
As for the fuel filter. I have only seen that once, and after that, I FILL my new filter with new fuel before screwing it on. One option you have is to open a fuel fitting after the pump and allow the pump to purge the line, but be VERY CAREFUL doing that. Petrol you know, she goes bang really easily! The only suggestion I have for that would be to make sure your batteries are fully charged and in great condition and just keep trying to get it to run....
Chris.........