Persitent engine alarm

[gkowalski]

Anyone have an idea how to isolate the cause for a persistent alarm . I have disconnected the leads from the senders and the alarm continues. I have also tried to short the sender wirefrom both  and it has no effect. My boat is 1989 MK1 with the  wiring change to remove the ammeter. Any ideas or tests I might try? Jerry Kowalski C34 981

[Ray & Sandy Erps]

My recollection from my backyard mechanic days is that most sending units are a variable resistor to ground.  The alarm, whether it be low oil pressure or high engine temperature goes off when the sending unit grounds the connection.  The low oil pressure sender grounds when there is no oil pressure and the high temperature sender grounds when there is high temperature.  If either wire to the sender is chaffed and touching the engine, you have another independent source to ground that needs to be ruled out.  Frankly, I don't remember if the C-34 has two alarms (one for each sender) or just one with a branched sender wire but I would start disconnect wires on the actual alarm rather then the sender. Find out which one is hot when the key is on and then start concentrating on the other wire by trying to follow it and look for a rubbed through spot, or check for continuity to ground, or bypassing it with a jumper wire to the sending units to try and determine if you have a grounded sender wire.  The fact that the alarm rings when the wires are pulled off the senders tells me the wires are shorted to ground.

[Ron Hill]

Jerry : I assume that it's your oil pressure alarm that's sounding.(your boat didn't come from the factory with a temperature alarm) Sounds to me like you need a new oil pressure switch. 
Look in the tech notes as I've published a recent Mainsheet article (Aug 2006) on that very item.