'90 Johnson 200HP faulty overheating/fuel restriction warning

I have a 1990 Johnson J200STLESE that I bought new with good maintenance. I'm getting a random overheat/fuel restriction warning...constant horn buzz which is driving me nuts. Inferred indicates no hot spots The horn beeps once when key is turned on indicating the system is working correctly. The horn may go off at anytime with a constant buzz, just never know when and at any speed. I've been out several times with no horn issues; last time out everything worked fine. The other day in the garage, just for kicks, I turned the key on to check it out and don't you know the horn began right off with that constant buzz. With the key on, I've disconnected the head heat sensors and grounded them out; each sets off the horn so they should be OK. I'm baffled by the fact that I can disconnect the brown positive wire on the oil tank and the constant buzzing stops; does that mean the oil tank senor is bad?
Without testing, I've received some diagnosis comments; one saying the horn is faulty the other saying the senor in the oil tank is faulty.... Thoughts anyone????