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Larry B.
Larry B., Marine Mechanic
Category: Boat
Satisfied Customers: 574
Experience:  Mercury/Mercruiser Certified/Verado/DTS / Yamaha Two and Fourstroke Certified 27 years experience
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I am working on a 2002 Yamaha 50 TLRA and have a very

Customer Question

I am working on a 2002 Yamaha 50 TLRA and have a very puzzling electrical problem. The problem is within the warning system, I believe. With all wiring connected, the buzzer sounds (even with the engine cold and not running) when the key is turned on. Once started, the engine runs in slow or kick down mode. If I disconnect the gray wire from the oil level sensor plug-in, the engine runs normally and the buzzer stops. The top thermoswitch when submerged in boiling water will not activate buzzer (neither will a jumper wire across its connections). This switch passes continuity/discontinuity tests. The bottom thermoswitch with pink and black wires does not react (it remains open) when put in hot water. A jumper wire across its connections will sound buzzer (gray wire still disconnected). Functioning thermoswitch (orange/orange-green) when moved to pink and black wires will sound buzzer when heated. Oil level sensor passes all tests. I have no tests for CDI box. What's up? Please help.
Submitted: 9 years ago.
Category: Boat
Expert:  Larry B. replied 9 years ago.
Hi , I have been looking at a manual on disc, and The thermo switch on top that you say will not set off the horn tells the cdi box when to come out of warmup mode,(the fast idle you get when you cold start). If you can turn off horn and rpm reduction by unhooking the gray lead then the problem is either in the hold circuit ( the hold circuit is there to keep the motor from coming out of rpm reduction if oil is added to the tank while running down the water and keeping someone from being thrown overboard) in the oil level sensor or a short in the harness/ or gauge if equiped. There are no tests for the CDI box listed in the manual, you test everything else and if all good replace the CDI (although I have never seen a bad one in 13 years of working on Yamaha product) The way I read it , with the float in the down position you should have continuity between Gray/black , pink/black, black and green/red, with the float in the up position you should have no continuity between any of them, there is a diode on the pink wire, Try between pink and green/red should be conyinuity only one way. And see if there is any continuity to ground on the pink wire while the sender is plugged in with rhe only connection to the pink wire being to the sender, the horn is set off by the pink wire being grounded.