No alarm on start up

[Sailm8]

Yanmar 2gm20F has always buzzed when the key is turned. Since the boat was hauled out, bottom painted and splashed after 3 weeks, it no longer alarms when you turn the key. The test switch shows lights and sounds the alarm. I have changed the exhaust elbow and replaced O rings in the top of the high pressure pump during the haul out but would not expect this to have anything to do with the alarm.
No obvious disconnected wires on the sending units for temp and oil pressure. Stumped as to what to check next and I've lost confidence in the alarms sounding when required. Suggestions welcomed.

 

[Allan12210]

Is there a buzzer check switch position? This would indicate a bad buzzer. On mine it shares the switch that turns on the instrument lights. With the key on, and engine off pull the wires off the senders (oil pressure and water temp). One of them removed should make it buzz. Then touch each to ground and one of them should make it buzz. If nothing the buzzer may be bad or both senders. If one makes it buzz, the other sender is probably bad. I think.

 

[Sailm8]

Buzzer works fine in the test position. I'll try the disconnect idea you suggested.

 

[Ralph Johnstone]

No obvious disconnected wires on the sending units for temp and oil pressure.

Most likely a wiring problem but start with the easy stuff first. Only the oil pressure alarm will sound when the key is turned. The high temp. sensor doesn't see a problem at this point in the game.

Turn on the key and try shorting out the oil pressure sensor first and then the hi temp. sensor. If you still have no audible alarm from either, it's a wiring problem.

If it is in fact a wiring problem, try going through it piece by piece with an ohmeter. I know that's not much comfort, but that's why they invented Jack Daniels .

 

[Bill Roosa]

The oil pressure switch (not the op gauge sensor) is just a switch that is grounded when the op is low (like when the engine is off). If you pull the op switch wire and ground it the buzzer should stop when you pull it ( no ground at that point) and start to sound when you ground it. If it sounds when the wire is grounded the check the circuit on the switch from the terminal to ground. it should read very close to 0 ohms resistance. If it does not the impact modulate the switch and recheck. If that does not work then take the switch out and test between the terminal and the threads. it should read 0 ohms. If it does not the switch is bad.
if the buzzer does not sound when you ground the op switch wire to the engine then there is a wiring problem. Since the motor starts the engine ground is probably OK. trace the wire back to the engine panel checking all the connections along the way. I'm betting that one of the quick connect plugs (there are several) has a corrosion problem.

 

[Apex]

check your grounds at the engine etc. I never had an alarm until I tightened the battery grounds (not hand check, pull, clean and install to torque)

 

[Sailm8]

Thanks guys, you've given me plenty to try. I'll be back if your suggestions don't work.

 

[Sailm8]

Update

Fixed the problem. The wire from the sensor found on the front of the engine below the alternator, had pulled out of the crimp connector buried deep in the engine. It was only difficult to find because i have an aftermarket smart charger and alternator and there are a host of wires and unused connectors mixed in. Thanks for all of the help.