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Adding a Tach

bill_w

bill_w

Advanced Contributor
I've got a 72 50 hp Evinrude I'd like to install a tach on. There is no plug on the remote control for one, so I guess I have to wire it in myself. Am I right in thinking I come off the yellow/grey lead from the stator at the terminal block for a signal, the ignition for 12 v, and a ground to the motor?? Also, can anyone tell me what to set the tach to i.e number of pulses??

thanks in advance
Bill
 
There is normally a "gray" wire inside the control box that is unused. This is the wire that leads to the engine and connects to the yellow/gray lead of the rectifier. If this wire exists within your control box (and it should), it will be the wire that is to be attached to the tachometer's sensor terminal.

If your control box is the older white type that has a lower plate on its side that is attached with 2 or 3 phillips screws, removing that plate should reveal the "gray" wire I speak of.

The rest of the wiring.... 12v supply to the tach attaches to the "A" terminal of the ignition switch. Ground wire leads to ground obviously. Light bulb wire, if it exists, connects to the proper light switch terminal.

Set the tach to #6.
 
I'll check inside the remote box...it's one of the stupid push button types for the gear selection, but I have a Johnson box I'm changing over to. And the sensor lead comes off the rectifier, not directly off the stator?

thanks Joe
 
Joe...no offense meant...just wondered how to tell how many pulses an engine puts out. Would a 50 hp 4 cylinder Merc put out the same as a 50 hp 2 cylinder Evinrude, for instance. I'm guessing its a measure of how many magnets are in the flywheel?
 
No offense taken. I was just stating without going into detail that each year, as something new came out and was explained in the OMC seminars, I retained the explanation. When the alternator system came into the game so to speak, it was stated that it emitted six (6) pulses which still holds true for the majority of the Evinrude & Johnson engines.

Some vary in their pulse range of which I have the bulletin (somewhere) but unless my memory is flawed, your engine's charging system delivers six pulses. I'll leave it to someone else to explain the magnet scenario.
 
Looking at the pic of the stator in the parts section, it looks like it has 6 poles. Assuming one magnet, crossing 6 poles would produce 6 pulses / rev? Makes sense to me, as would the 6 diodes, one for each pole. Just my wild stab at electronics.
 
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