[ttop5.0]

ok can anyone tell me why we are supposed to hook up an autometer tach to the negative side of the coil, i thought that was supposed to be aground? How are you supposed to get a reading from a ground????

[Darrell]

The negative side of the coil is pulses which triggers the tach. Its not a ground, its negative.

[Milner62]

well Im going to say the same thing but look at the old breaker point dist`s. the negative coil wire runs to the points, the negative is what controls the firing of the coil on the breaker point dist, when the point opens on dual points one charges the coil up (the common step-up coil) then when the second one opens and breaks the contact it causes the coil to fire through the post to the dist rotor arm. Same basic setup in modern electric and hei dist setup. My mercury has a factory tach and has 2 wires that hook up to the negative on the coil and two on the positive (one from the positive comes from the key switch and the other one runs from the post on the coil to the solinoid on the starter so when you crank over the engine it fires the coil and gives power to the starter)

[Bossman351]

If you have an MSD you need to plug it into the MSD box and not the coil.