Oil alarm still sounding

Howdy. I have a 1988 Mariner 150, it's had a charging problem which is fixed now. It's also had an oil alarm issue which I am trying to work through. The marine shop tested the alarm systems while it was there but said they were all ok. The alarm only beeps intermittently after about 15 mins of running, then becomes a continuous beep beep beep after about 20mins. Then will still beep when the key is turned on whether the engine is running or not.
Top oil tank is completely full and I have tried another top oil tank cap/sensor but still the same result. Plenty of oil getting to the engine also. Any other thoughts? Any suggestions on ways to test the oil pump pressure sensor as the Marine shop is sending me broke.
Also, the new rectifier/s installed have stopped the rev gauge going over 4000rpm, :facepalm: But when I hit the trim switch, it reads correctly for about a second? Help!
Many thanks. Rich.

Re: Oil alarm still sounding

First place I would check is in the remote oil tank (boat side) and make sure the cap is not broken and is securely tight. Second I would pull the cap with the hoses out and inspect the filter on the bottom and make sure their is no debris or "sludge" on the intake filter. If all of that is clear proceed with this:

Re: Oil alarm still sounding

Thanks very much. It's either number three in the list or a faulty alarm module. Trying to find another module to test now.

Re: Oil alarm still sounding

Hi again. Just a question with checking the oil tank filter. If I pull it out, is there any danger of oil running out and air going into the tube?

I had this happen on a 2 stroke motocycle which ran out of oil, then when the oil tank was re-filled, didn't flow as air was caught in the system and had to be bleed out before it would work again. Many thanks. Rich.