Troubleshoot continuous warning horn MC 5.0

[Phranco]

So my 2000 Bayliner 2455 Ciera with Mercruiser 5.0 Alpha is in good shape but other day the warning horn started going off continuously. I checked and see that there are three conditions that will cause the alarm to sound.
1. Engine temp (gauge works and the temp rises after starting the engine and stays in the normal range)
2. Engine oil (gauge works and quantity is fine)
3. Drive lube level (serviced a year ago and no known reason for it to be low)

I would like to figure out which sensor is causing the horn by individually disconnecting each sensor so that it is no longer providing a signal to the horn. This way I can either replace the bad sensor or fix the issue whatever it is.
The boat is in the water so I would like to start by disconnecting the engine oil sensor, then the temp sensor. Two out of three will allow me to know which sensor is sending the signal to the horn.
Can anyone tell me how to bypass these sensors? I know where the engine oil and temp sensors are but I don't know about the lube level sensor. I also don't know if simply disconnecting the bad sensor will silence the alarm or cause it to stay on.

Thanks for any help!
Frank

 

[Bondo]

Can anyone tell me how to bypass these sensors? I know where the engine oil and temp sensors are but I don't know about the lube level sensor. I also don't know if simply disconnecting the bad sensor will silence the alarm or cause it to stay on.

Ayuh,...... Welcome Aboard,...... All 3 alarm switches have a tan/ blue stripe wire, when the switch goes to ground, the alarm comes on,.....

The drive lube bottle switch is the tan/ blue stripe wire to the lube bottle,......

The temp switch is in the t-stat housing,......

The oil pressure switch is most likely on the port-side, mid-way, at the bottom of the block, just above the oil pan,......
While rare, it could be center aft top of the motor, behind the distributor,....

Just unplug each 1, til the alarm stops,.....

 

[Phranco]

Thanks Bondo,
Yesterday I unplugged the water temp and the oil pressure (yes, port side engine block). Horn still blasting. I'm so stupid I didn't realize the drive lube HAD A RESERVOIR. I'm heading down to check that now and I'll get back to you with the results. Really appreciate the info, this should be all I need!
Frank

 

[QBhoy]

My first port of call would be the gear oil reservoir. My boat certainly needs a few top ups over the season after changing it fully. There is always a gap or void between the header tank and the level you fill the drive to, if you drain the full system, header tank and all. Takes a while to settle out properly.

 

[Phranco]

Thanks guys! It WAS the gear lube, down towards the bottom of the reservoir and one minute later I was back up and running with no warning horn. AND I learned about the warning horn system which has been on my to-do list for years.
Frank

 

[Bondo]

My first port of call would be the gear oil reservoir. My boat certainly needs a few top ups over the season after changing it fully. There is always a gap or void between the header tank and the level you fill the drive to, if you drain the full system, header tank and all. Takes a while to settle out properly.

Ayuh,...... I fill the drive through the drain screw, til oil comes out the vent screw, which I put back in, then continue filling til the high mark on the bottle,.....

All full in 1 shot,.....

 

[QBhoy]

Ayuh,...... I fill the drive through the drain screw, til oil comes out the vent screw, which I put back in, then continue filling til the high mark on the bottle,.....

All full in 1 shot,.....

Bondo. I do the exact same but let all the oil drain out the bottle too first. Takes a day sometimes or at least overnight.
Fill it up from bottom until out the vent screw (as you say) then fill the bottle. There is always a void between the vent screw and the bottle.
After an outing or two...it needs topped up again. The oil obviously finds its way down and drops the level in the header. If you know what I mean.

 

[QBhoy]

Thanks guys! It WAS the gear lube, down towards the bottom of the reservoir and one minute later I was back up and running with no warning horn. AND I learned about the warning horn system which has been on my to-do list for years.
Frank

Excellent. Thought it might be this.