Oil Pressure Switch - Universal 25XP

[jim flynn]

I just installed a new buzzer alarm in the instrument panel of our 1988 Catalina 34 with a Universal 25XP engine. The alarm has two grounds - one gives a constant alarm and the other gives a pulsating tone.

I installed an aqualarm temperature switch to the engine manifold and grounded one side of it to the engine block and the other side I connected, via a new wire, to the constant sound negative connection on the alarm.  I did the same thing for the oil pressure switch, this time using the pulsating negative connection on the alarm and the existing wire leading from the oil pressure switch to the instument panel.  I checked this wire for continuity - AOK.

My problem is that I don't know how to test the oil pressure switch itself.  I assume the switch is grounded until the engine develops sufficient oil pressure to break the ground connection.  Therefore, if I activate the alarm with the ignition on and the engine off I should get an alarm - I don't.  Are my assumptions correct?  Do I need a new oil pressure switch?  If so any hints as to how to get at it?  Thanks for any advise you may be able to give.

[Ray & Sandy Erps]

Your assumption sounds good to me.  You could take the wire off the oil sending unit and touch it to ground.  That's the backyard mechanic way.  It will either buzz or spark and blow a fuse.  A garage mechanic would put an ohm meter on the sending unit and see if there is continuity to ground when the engine is off and see if there is an open when the engine is running.  A smarter mechanic would look at the wiring diagram for a clue to see if it shows a ground symbol for the pressure sending unit.  I'm all for touching the wire to ground to see if it sparks.  Fuses are cheap. :)

[jim flynn]

Ray
Thanks for the suggestions.  I'll give them a try this weekend.
Jim Flynn