wiring a generec tachrometer into a Mercruiser.

[johnbell47]

Tach wasnt working on my Century with alpha one gen one 5.7 mercruiser. I bought a generic tach on E bay that most closely matched the old instruments appearance. I have wired a bazillion tachs in the past and never had a problem. now I do. I have always wired, minus to ground, plus to 12 volt, pulse to negative side of the coil and of course the lighting circuit. This tach wont work wired that way, the instructions do not mention the coil pulse but does mention a "W" terminal on the alternator. Looks to me like if I wire to the alternator, I am going to have to calculate how many pulses per rpm, pulley ratios, etc. has anybody ever delt with this before?

 

[Alumarine]

Are you sure it isn't a 2 stroke tach?

 

[Scott Danforth]

Agreed...do you have the right tach