Mercury Mariner Outboard 100hp alarm - Newbie needing help

Hi, I have a 1989 Mercury Mariner Outboard 100/115hp model 11004129D on a Vanguard Phantom. Last time I took it out it ran fine. Then started beeping. Fast beep, about 3-4 beeps per second-continuous non stop or break. Stopped, turned engine off, and checked the oil tank under the cowling and was low. Added some. Started up again and still beeping. I turn ignition on and hear the usual start up beeps. After the normal beeps it continues to have the fast beep alarm before even turning the engine over. The unit came with no manual. I was just coming in to the ramp, thank goodness. End of the trip. Can anyone help me out? Take it in for service? It's a 6 week wait list.

I've been searching other posts regarding alarms. The cap, the sensor, over heating, etc. But I thought I would ask specifically to my model and year. After getting home I put the key to on to hear the system startup beeps and afterwards the fast beeps still there (thinking it may just have overheated but beeps still there 2 hours later out of the water and no didn't turn engine over).

Any ideas? Thanks everyone!!!

There is only two "things" that your warning system checks - oil level and block temperature.

The sensors are basically simple switches that work on resistance. Zero resistance turns the switch ON and you get beeps.

The oil tank sensor is mounted in the bottom of the oil tank and a "float" provides the second part of the circuit. When the oil level gets low enough, a magnet in the float contacts the sensor = beep.

The temp sensor is a simple resistance type plug - the warmer it gets, the lower the resistance. When it gets "hot", resistance goes to zero = beep.

Both of these (sensors) are prone to failure. The float sometimes breaks and the oil circuit is completed. The temp sensors wear out, mostly because of the simplicity of the circuit (particularly if you live in a northern climate you would be aware of the failure rate of the thermostat in a car - same technology, same issues).

Mercs of this generation are "known" to have temp sensor issues in particular with broken oil floats a close second.

There is also, to a lesser degree, the possibility that your alarm module is toast (but either other condition would be significantly more likely).

You can try some "easy" trouble shooting to see if one of the sensors is the problem.

The temp sensor is located on the (head) - it's just a little plug in the block with a single black wire coming from it. The wire will go down to a junction that marries up with a tan, tan/blue and another black wire. If you disconnect the wire, that comes down from the sensor at that little (block) and your alarm goes away - with key on, motor not running - your temp sensor is shot.

To test the oil level sensor, look "under" the tank. There is a pair of blue wires that go into (two) bullet connectors - simply pull one of the bullet connectors - again, key on, motor not running - no alarm = oil level sensor is shot (greater possibility it's the float than the sensor in the bottom of the tank) - unless something has changed you may have to replace the entire tank to cure this issue = $$$ (not something I would do - this alarm is only for "oil level" NOT whether or not the oil pump is functioning - so I would leave it disconnected and simply top up the oil before each outing. A full tank of oil on this model will give you about 6 hours of running time at Wide Open Throttle - you would likely run out of gas long before you ran out of oil).

If you still have the beep - disconnect both sensors - if the alarm remains, it is the module itself.

Hi Graham,
Thanks for your help. Finally got around to it. Disconnected one of two bullet connectors under oil reservoir and beeping stops. Thanks a lot for your detailed help!
Another question, any issues with leaving one of the two bullet connectors disconnected? Just leave it or protect it in tape or an empty connector, does it matter?

When I used to turn the key I would get 3 beeps. If I remember correctly it was one beep then 2 fast beeps. Since the sensor fail it was one beep then continuous fast beep. Can I assume the original 2 beeps after startup was the oil sensor self test? No problem not hearing it? Checking the oil level during operation and top up before every trip is what I was doing originally, LOL, never knew there was a low oil sensor.

Again thanks for the help!!!! You saved me so much money!