How to Repair a Yamaha 300-Amp Motor Controller

The Yamaha outboard motor uses a 300-amp motor controller, or motor control unit, to run alternator-powered discharge systems, as opposed to distributor type systems. The motor controller, which is actually a capacitor, converts alternating current from the coil to direct current used by the spark plug. This charge is delivered to fire the right cylinder in the correct firing order. If the motor controller goes bad, it needs to be replaced.

Instructions

1

Remove the Yamaha's negative battery cable with a wrench.

2

Locate the black and yellow wire that is attached to the ignition coil. This is the capacitor, or motor controller's lead. Trace the wire to the motor controller.

3

Lay the metal tip of the screwdriver across the motor controller terminal lead. This will discharge the motor controller.

4

Remove the lead from the motor controller with the screwdriver. Pull the old motor controller out by hand and set the new one in place.

5

Connect the lead to the new motor controller with the screwdriver and then replace the Yamaha's negative battery cable with the wrench.