will the tach from 1961 johnsons 20hp work with my 1991 40hp johnson

[MudLake]

I may decommission 2 20hp johnsons on my 15 ft starcraft for the 1991 johnson 40 hp which i rebuilt 20 thou over.
My boat has two tachs for my 1961 johnson.
I got the omc control with the 40 hp and it has a 3 pin connector on it for
acc, gnd, tach signal.
I hooked up my fluke meter to the tach pin and it reads about 142.
if 142 low for this engine.
question: will the 20hp tach work with the 40 hp outboard??????????

cheers

[F_R]

Absolutely not. But don't dispair, those tachs are in big demand. They are driven by the magneto, and are no longer made. Somebody wants them.

You need a tach that is driven by the alternator, which is where that grey wire goes.

BTW, 142 volts is way wrong. You probably have a blown rectifier. Should be close to 14 volts.

[MudLake]

Maybe not clear on the 142.

my meter was on frequency so it would have been RMPs