TACH questions - '81 90 HP

[metriccrescentwrench]

I want to add a tachometer to my recently purchased boat.

In outboard terminology is "12 Poles" the same as "12 Pulses"? What will I need for my motor?

On the 3 pinned plug that's beneath the throttle friction lock, it's got the purple hot wire on it but not the grey tach signal or the ground. I can probably locate pins that will fit the plug but need to know which signal wire goes to which position.

thanks

 

[guy74]

Re: TACH questions - '81 90 HP

Hi,
Your motor is 12 pole, which means you need to set the tach for 6 pulses. The wiring on the plug should be BLK-GRY-PUR, looking at the rear of the control. The center gray wire in the plug is toward the bottom.
Sincerely,
Brian

 

[metriccrescentwrench]

Re: TACH questions - '81 90 HP

Thanks Brian.

So then, as a check of the tach's accuracy, I should be able to use the frequency counter on my multi-meter and divide by 6 to get the engine speed, right?

 

[72SideWinderSS]

Re: TACH questions - '81 90 HP

Thanks Brian.

So then, as a check of the tach's accuracy, I should be able to use the frequency counter on my multi-meter and divide by 6 to get the engine speed, right?

Freq. X 10 = RPMs.
I use a signal generator to calibrate my tachometer.

 

[metriccrescentwrench]

Re: TACH questions - '81 90 HP

Freq. X 10 = RPMs.

Duhhh. I knew that Minutes. Seconds. Almost the same.

I use a signal generator to calibrate my tachometer.

Geeze, I should have thought of that. Peice of cake then.