Warning horn constantly on even before engine starts

[JimMM]

Hello. The warning horn on my 1994 200 HP carb Mercury outboard faintly sounds when I turn the key on. Sometimes I have to wiggle the key to get it to sound and also to get the two beep test signal. Once the engine is started the constant beep does not stop. Temp never gets above 120F at idle and water starts coming out the telltale when it warms up. Hottest it gets is 180 at 1/2 throttle off plane. Once planed the temp drops back to 120F. Every now and then at full throttle, the oil warning beep beep beep will start sounding, very loudly. The oil injection pump crankshaft gear stripped earlier last season so I removed the shaft and put the pump cover back on with a new gasket. I put a tiewrap on the local oil reservoir shaft to keep the float from dropping. It is still there and holding the float up. I am running Mercury oil 50:1 premix.

One other associated thing that might be a clue. When I first turn on the key before the engine starts, the tach will start going up. It gets to about 2500-3500 RPM reading and stops. This is before I start the engine. The tach is reading 2-3k RPMs but the engine is off. Once I start the engine it drops down to around 800 and starts reading the actual RPMs idle. It will read fine up through WOT. The overheat constant on warning is very faint, about 1/10th as loud as the oil beep beep beep warning.


I know I can disconnect the buzzer but I'd like to find out what is causing this problem and leave the buzzer connected in case some day the engine really does overheat.

 

[joed]

Commonly this is cause by the oil tank level module.

 

[JimMM]

Thanks, I take it you mean the module that monitors the oil tank level under the cowling, not the remote tank? I have the float wired in the up position. Disconnecting the wires from the cap have no effect. If I disconnect the module will I also lose overheating warning beeps?

[EDIT] OK I disconnected the wires to the oil warning module. Disconnectin the Blue, Blue/White and White wires from the oil level cap and oil pump rotation sensor had no effect, but when I disconnected the Tan/Pur wire from the terminal block above the ignition plate on the starboard side of the powerhead, the beeeeeeep stopped.

Out of cuioustiy I reconnected the Tan/Pur wire and the beep started again, so I then disconnected the Pur wire but no change. So I reconnected the Pur wire (is that power to the module?) and disconnected the Tan/Pur wire. I reconnected power to the module in hopes the over temp warning will still work. Unless I intentionally run the engine out of water I have no way to tell if the overheating beep beep beep warning will work.

Since the plastic gear for the oil pump has sheared and I'm using premix 50:1, will I need to replace the Oil Warning Module (I heard they are expensive like 100s of $$) to just have over temp warning even if I don't need no oil warning? I think the Pur/Tan wire I disconnected is what goes to the buzzer in the control box so in effect I've disconnected the buzzer?