tach install, 1965 100hp V4

[68C15]

I have a used tach from a 2 stroke I got at a local car junk yard. the donor boat/Mercury 50HP looks to be mid 80s. it had a harness that plugged into the controls with 3 wires. the back of tach has 3 studs. BATT, GND, and ALT. the first 2 are a no-brainer, but the ALT stud has me and my automotive mind stumped. I do not have a wiring diagram for my motor but the wiring is unmolested.

where or how do I hook this up or is it the wrong tach?

thank you for any help

 

[F_R]

Re: tach install, 1965 100hp V4

First thing you need to do is figure out what motor you have. There is no such thing as a 1965 100hp. Come up with a model number.

A generic answer to your generic question is that tach probably won't work---again depending on what motor you have.

 

[68C15]

Re: tach install, 1965 100hp V4

sorry there. the motor is 1 year newer than the boat.
1966 Johnson Golden Meteor 100HP, model V4ML-12M with battery ignition, and electric shift.

 

[Chris1956]

Re: tach install, 1965 100hp V4

That tach probably won't work. However, an automotive-style tach might, because the ign system is very similar to a 60s-70 car. Try a Dewll/tach, if you still have one laying around and see what happens. A 4 cylinder 2 cycle OB will mimic a V8 automobile engine.

 

[F_R]

Re: tach install, 1965 100hp V4

Yep, you are in luck. An automotive tach for an old points-and-condenser type V-8 car will work.

 

[68C15]

Re: tach install, 1965 100hp V4

sweet, thanks guys. I have a couple of those laying around.