how is the tach hooked up on a merc?

[vroom ZOOM]

Hello

would anyone know how the tach is hooked up on a 1987 merc 2.5? is it hooked up to the alternator or coil? also, what kind of voltage is going through it and what frequency? thanks

 

[Scott Danforth]

its hooked to the negative side of the coil (its the grey wire)

pulsing ground signal - 1 pulse per each cylinder firing

 

[achris]

Coil negative, 2 pulses per revolution for a 4 cylinder.

 

[vroom ZOOM]

ok thanks