Picked up a Bass Tracker pontoon with 96 Mercury 115 on it couple of weeks ago. Started the motor up with ear flaps and everything sounded good when l bought the boat.
Took to the lake last week and put in the water. Boat fired right up ran fine. Alarm came on after just a minute or 2 and will not go off now. Stays on all the time now if the key is turned on.
l know l have good water pressure and motor is not hot.
l am 99% sure that l am getting oil injection, but added oil to the gas just to be safe until get this issue lined out.

What else will set off alarm?
What should l check?
Thanks

Solid alarm over heat> beeping oil> There are some sensors Make sure when you took the cover off it did not snag a wire and disconnect it>

Ours did it this weekend too and it was low on oil. The dealer said the oil mixes automatically with the gas (4 stroke). Once we put oil in the beeping stopped.

How did u determine it is not overheating? Cylinder head temp can be measured with an infrared temp gun or thermomelt stick (available at ishopmarine.com), should stay below 165º or so.

The alarm is a peizo buzzer in the control box, with 12V coming from the purple accessory wire, & grounded by a tan wire attached to 2 temp switches (one each cylinder head) & the oil sensor. Could be a wiring fault along there shorting the tan wire to ground.

The temp switches r at the end of tan wires near the top of the cylinder heads. By disconnecting these one at a time while the alarm sounds, u can determine which one is malfunctioning.

You can test the switch in a pan of water on the stove with a kitchen thermometer, using a multimeter or test light & 12V power source. Switch should close at around 165º F.

[Note to mary: u misunderstood what ur dealer said; oil is not mixed with gas in a 4-stroke engine]

If your motor is squirting water when running, the water pump is working. The only two alarms on mine are for low oil and overheating due to the water pump not working properly. A friend had that problem and it was a sensor.

Most likely a faulty low oil sensor, located in the resevoir tank. These get gunked up over the years. See your service manual for testing procedures.