rev counter wiring Evinrude 90 4 cylinder

I want to add a rev counter to my boat. Am I right in believing that the three 'spare' wires from the remote can be used for this? I think they're purple grey and black.
Also, will any conventional rev counter (positive, negative, signal) work with the magneto ignition system?

You didn't state the year of that 90hp, however, the answer to your question is "yes".

Black = Ground lead. To tachometer ground (G) terminal.

Gray = Signal lead from rectifier. Attaches to tachometer sensor (S) terminal.

Purple = 12v source, hot only when key is in the RUN or START position. To tachometer voltage terminal (B), (+), whatever it may be marked.

That engine will have a solid state ignition system (Magneto Capacitance Discharge), meaning it is a solid state ignition system but self contained, supplied by AC power generated by the stator under the flywheel (keeping it simple).

As such, you willl need a tachometer that operates off of the engine's alternator charging system. It usually has a dial on the back that you set to a specific number.... on your engine, set it to number six (6).

The above assumes that your engine is indeed a "Magneto Capacitance Discharge" ignition model... anything after 1973.

Thanks for the reply mate. Sorry, it is a 1982 powerhead, with the solid state ignition as you say. Just wonder why I would set the tacho on '6' when it's a 4 cylinder engine?

realslimshady said:

Thanks for the reply mate. Sorry, it is a 1982 powerhead, with the solid state ignition as you say. Just wonder why I would set the tacho on '6' when it's a 4 cylinder engine?

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That confuses a few other boaters too. The tachometer gets set on #6 due to the fact that the tachometer operates off of the engine's alternator charging system which emits and the tachometer demands (are you ready)..... six (6) pulses.

ok, cool. thanks

kimcrwbr1 said:

I allways wondered about that is it 6 pulses for one revolution? That would make 30,000 pulses per minute at 5,000rpm

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Nobody cares... It works... that's what counts.

There's six magnets in the flywheel therefore position six. On the smaller motors with five magnets in the flywheel, position five.