I have a Yamaha 90TLRU with the 703 controller on my Duracraft aluminum boat. Some time ago I noticed a spot of oil on the concrete under the motor. Investigation revealed the source of the leak coming from the oil sensor’s rubber cap on the 2-stroke oil tank. While the boat was out from under the carport, I thought I would exercise the motor as it had been sitting for about two months. Turning on the ignition switch, the alarm buzzer came on immediately. I have a service manual and looking at the troubleshooting chart, one of the possible problem items causing the 'Irregular Warning Indication' is the oil level sensor, and assuming that this was the problem (due to the leak), I replaced the sensor with a new one. I also replaced the entire oil tank and associated components. I tested both the upper and lower float switch position with my Fluke before installation and everything looked good per the manual. That took care of the leak, but the buzzer still sounds when I turn on the ignition. When I raise the motor to its top position, the oil level drops in the rear of the tank, the float moves down its stem and the buzzer stops. As soon as I lower the motor again, the rising oil level pushes the float back to its top position, and the buzzer comes on again. Why would the buzzer sound if the oil tank is full?
I have also checked the thermo switch’s operation per the shop manual – it works perfectly as the water bath temp increases and decreases. I don't think my problem is related to the water cooling circuit, as the buzzer sounds as soon as I turn on the ignition, when the engine is completely cold.
I have checked all the wiring and harness, and everything looks good – no corrosion nor any loose connections that I could find.
My boat does not have an oil level warning lamp in its instrument cluster, so I don't think that buzzer is related to anything in the wiring to the cluster.
The only remaining item in the trouble shooting chart that could be causing the buzzer is the CDI unit. This baby costs about $500.00 to replace and I want to be sure that it is in fact the problem before I drop the moola. I have searched this forum thoroughly and could not find anything I have not checked. Can anyone throw any more light on where else I could possibly look?
as your boat wasnt rigged with the correct instrumentation its hard to say.
the horn will sound for several reasons and with the correct rigging components the visual will indicate what caused it.
however I think your gonna be fighting a sensor issue in the tank. test it with everything installed.
Rodbolt, I had my fingers crossed you would respond - thanks for doing so this promptly! Could you clarify for me what you mean by 'test it with everything installed'?
I cant remember all the wire colors, but with the oil tank assembled and the engine level test the oil tank switch resistance with everything installed.
best I remember your engine also uses a thermo switch, its either on or off.
I dont see a lot of small engines so I have to think hard and this morning hard thinking is killing me
With everything installed, oil in the tank, engine level, I tested the restistance between ground and the green wire - got 0 ohms, as the manual says it should. The other wire is green/red, but that one is for the lower float position that closes the switch when the tank is empty. This indicates the oil float is in the upper position as it should be, closing the circuit so that the buzzer sounds. I can't figure out why the buzzer sounds on a full tank of oil. Does it do this as a confirmation, then cut off when the engine starts? Should I just try and start the engine to see if the buzzer goes off when it runs?
there is no self test on that motor.
either the sensor switch in the tank is bad or the thermo switch is bad.
the thermo switch is the one with the pink and the black wires.
Figured it all out. The Green and Green/Red wires coming from the Oil Level Sensor only serve to provide the oil level indication on the digital tachometer, which I don't have. I left these disconnected. The Pink wire provides the low oil level indication to the CDI unit, which will slow the rpms down to 2,000, and it also goes to the buzzer so that it will sound upon low level. I confirmed this by letting oil flow out of the tank through the balancing tube, and sure enough the buzzer came on when the float reached its low level position. I also confirmed that the thermoswitch sounds the buzzer by shorting its two wires - Pink and Black. Used the wiring diagrams in the service manual - would have taken much longer without them. This would have been much easier to figure out if the digital tach had been installed originally, as it also has trim position, oil level indication and an overheat warning light.
Yamaha 90TLRU warning buzzer
and this morning hard thinking is killing me 
Linear Mode
