Steady Buzzer Sound

[johnmsch]

I have a 1994 Chaprarral 2130 Sport that I bought new and have kept it in my garage ever since I took delivery. I only boat in a freshwater lake, wash and clean it up after every trip, so this issue should not have anything to do with corrosion.

The boat came with the 7.4L Mercruiser which threw a rod at the end of 2020 with almost 1,200 hours on the engine. A friend recommended a guy who builds high performance engines for boats and race cars. I looked into that and for just a bit more money than doing a complete rebuild, as of March 2021 I now have a cusotm-built 496 stoker engine. Everything ran great all last summer, but at the end of the season, an electrical issue started happening that I can't figure out. Coming home from the lake, I stopped to top off the tank and heard the buzzer. This is the one where if you turn the key on and don't crank the engine within about 15 seconds, it goes off. The only way to stop it was disconnecting the positive cables from the battery.

Over the winter, I was passing by a West Marine store and picked up a new ignition switch. Yeah, I know that when there's a problem, you don't just start swapping parts but the switch was only around 20 bucks and seemed a good place to start. Put the new switch in and yep, same problem. I have traced all the wires from the ingition swtich and don't see any shorts or bare wires rubbing up against anything sharp.

Any ideas what to check next? I seem to remember reading something a long time ago about the starter solenoid causing this issue?

 

[Chris1956]

Those MerCruiser warning systems detect overheat and no oil pressure. Hence, the oil pressure switch is supposed to turn the alarm off, when it opens due to oil pressure. If your boat has a oil pressure gauge, then it will have two oil pressure sensors. They do not last forever. The one for the alarm is usually on the rear of the block, roughly the shape of a York peppermint patty, with a single wire.

Also the temp switch will trigger the alarm when it detects overheat. If you boat has a temp gauge, then it will have two heat sensors. They are usually on the thermostat housing.

 

[johnmsch]

Thanks for the reply @Chris1956, but I see now I didn't describe the issue well enough.
As soon as I reconnect the red starter cable to the battery, all the console lights/gauges come on. Its just as if I had turned the ignition key to the On position. After about 15 seconds, the buzzer comes on. That's why I initially thought the problem was with the ignition switch.

 

[Chris1956]

Those Mercruisers have a single plug that connects the boat to the engine. If the wiring on that is not the issue, and you installed the ign switch correctly (3 wires, power, starter solenoid, accessory/ign), I am not sure what could cause it. If you disconnect it and the alarm still sounds, you know the issue is in the motor wiring harness, or there has been some modifications made to the boat wiring. Also disconnect any other wires on the battery, not used to start the engine. Maybe one of those wires is supposed to be a ground, and you have it on positive, so power is going thru the nav lights/blower/bilge pump ( or something) and powering the accessory/ign wire? Electricity is happy to flow in either direction. A guess.

Another thought...It would appear that the battery is directly connected to the accessory/ign wires. The starter slave solenoid would only be connected to the starter solenoid wire, if it was somehow stuck, powering the primary winding. Not even sure how that would happen.

Your best bet is to get a MerCruiser wiring diagram for your year and model motor and see if there are any parts of the engine (CDI amplifier system perhaps) that have direct battery power. Then see if these are connected to the accessory/ign wire. Maybe one of those items is defective? It is just a SWAG.

You also might look for a broken or corroded ground wire. I cannot think of a particular culprit, but if one side of a circuit is supposed to be grounded and isn't power could feedback to the accessory/ign wire, somehow...maybe

 

[Chris1956]

Something else I thought of. If you pull the main plug the buzzer may stop, since it is disconnected. In that case, you will need to look for voltage on the accessory/ign wire at the engine plug. I would expect the wire to be purple.

 

[johnmsch]

Forgot to update this thread after finally figuring out the issue.
There is a clip on the side of the engine block that holds up the wiring loom behind the alternator. The clip was loose enough to allow the loom to sag down, which caused the orange alternator wire to just barely rub up against one of the studs on the back of the alternator. The wire was just barely punctured by that stud, but it was enough to cause the short.
I appreciate all the hints and tips!