1989 Mercury XR2 150 random beeping from buzzer

When the switch is turned on i have 3 short beeps. This i understand is normal. The motor has very little hours on it, but run it about 3 times per year since 2010. I do several times per year hook a flush fit to it and just run it for about 10 minutes. In 2010 launched the boat and started down the river and in about 2 minutes starting having short beep beep beep for about 2 miles to fishing hole. Soon as boat sits down beeping stops. Several days ago done the same thing. The water pump is shooting a steady stream of water, and lots of smoke is coming from exhaust when engine is running sitting still. The water pressure gauge goes up and holds there the entire time. All of a sudden the beeping came on and stay on until i pulled back on throttle and sat down. I moved around several times and never beep again. At the end of day i was 3 miles from ramp, fired motor up, water streaming out of hole and ran 45 mph all the way back to ramp, no beeping at all. Listed below are a few things i replaced on engine.

1. The wiring harness that goes to side of motor back to the small oil bottle on the engine. The cork gasket on this tank was cracked and the cap also. When this was replaced a fired the motor back up so oil would fill tank back up.
2. Water pump and impellar has also been replaced.

Any help would be appreciated.

Just a shot in the dark...check inside of the water fitting for the pressure gauge. You don't use it very often which allows crud to build up in the fitting.

The fitting you are talking about is this where it connects to motor or at the gauge. Had a dealer in our area say that it might be a sensor for the oil pump. He also scared the heck out of me. he said these motors have a plastic wheel in the crank that has always gone bad on these motors. He said this wheel pumps oil to the block?????????? He said he would have to pull the power head off to get to this gear. he would be able to look at the walls of motor and determine if motor needs to be rebuilt He said it would cost about $4,000.00 to rebuild this motor. I am telling you this motor has not been abused and only about 150 hours on it. This is the god's truth.

Check the fitting on the motor. Another boater had a steady alarm and found a defective oil level switch.

How about the oil level in the tank on the engine? When the oil level gets a lil low, the alarm could be going off. I had a problem like that once. With the engine running, slighty open the cap til oil gets to the top. Or you could pour some in with the engine off. Hope this fixes your problem...BF