Yamaha 90-HP Won't Shut Off

Electrical and electronic topics for small boats
KSavidge
Posts: 1
Joined: Mon May 30, 2022 10:58 am

Yamaha 90-HP Won't Shut Off

Postby KSavidge » Mon May 30, 2022 11:08 am

Q1: how can intermittent electrical problems related to the ignition key switch and trim switch for my Yamaha 90-HP two-stroke-power-cycle engine be repaired?

BACK STORY
On my MONTAUK 17, the Yamaha 90-HP two-stroke-power-cycle engine starts easily, but in the past on rare occasions the engine will not shut off when the ignition key is turned [to OFF from RUN position] or the [engine safety shut off switch] is pulled. Also in the past on rare occasions the engine TRIM switch on the throttle handle of the remote control does not operate the power trim. In the past if the ignition key switch is operated repeatedly between RUN and OFF, these problems resolve themselves.

At the present, the engine will not shut off with the ignition key switch or the engine safety shut-off switch. The trim switch works. [Some element of the electrical circuit referred to only as] connections appear intact and no corrosion is visible. In regard to electrical circuitry I am a novice.

jimh
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Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
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Re: Yamaha 90-HP Won't Shut Off

Postby jimh » Tue May 31, 2022 6:25 am

For a typical classic two-stroke-power-cycle outboard engine with a permanent magnet alternator (PMA) generating the spark voltage, the engine can only be shut off by a rather brute force method: the ignition key switch and the safety engine shut-off switch both use a circuit that suppresses the generation of the spark voltage by simply shorting the primary spark coil voltage to ground. Based on your narrative of the behavior of the engine, the inability to shut off the engine is due to a failure to stop the spark voltage from being generated.

The circuit that stops the spark voltage is typically found in the ignition key switch and the engine safety shut-off switch. I believe that in the rigging for your Yamaha engine these two switches are integral to the ignition key switch assembly. On that basis, the most reasonable inference about the cause of this behavior is a fault in the ignition key switch assembly, or a fault in the wiring that brings the engine shut-off circuit to the ignition key switch assembly, or a fault in the ground circuit to the ignition key switch assembly.

A further hint to what may be the problem is the associated intermittent operation of the throttle handle engine trim switches. Typically these switches apply a ground to either the UP RELAY or DOWN RELAY coils that control the trim motor.

On a Yamaha engine, the conductor wire insulation color used are given in a REFERENCE article at

https://continuouswave.com/whaler/refer ... e.html#Yam

According the usual wire insulation colors used by Yamaha, the wire color associated with the ENGINE STOP CIRCUIT has WHITE insulation. The conductor associated with the GROUND (or battery negative) has BLACK insulation. Check these two circuits at the ignition key switch. When the engine is running, be careful with the WHITE conductor; this circuit has several hundred Volts AC on it.

Having owned two Yamaha classic two-stroke-power-cycle engines, the operating manual for the engines included a very complete pictorial diagram of the electrical wiring between the engine and the remote controls and ignition key switch. Consult this diagram to verify the wire insulation colors and identify the circuits on your particular installation.

Many times a very close visual inspection of electrical circuitry can reveal a problem.

Because the ignition key switch and engine safety shut-off switch are in one assembly, a fault in that assembly could be the cause of both the ignition key switch and the engine safety shut-off switch not working, or the problem could be outside the ignition key switch assembly and be caused by a fault in the wiring.

A fault in the ignition key switch can occur, particularly if the switch is not well protected against ingress of water, as might happen on a small open boat with the helm console unprotected by any enclosure.

To deduce which circuit element is the cause of the NO-STOP condition cannot be done without having physical access to the wiring and the switch assembly, so my advice ends here.

Operating the boat when the engine safety shut-off switch is not working is dangerous. You should remedy this problem before further use of the boat.