Mopar Muscle Association UK

Ive decided to fit a Autometer Tach to the Challenger, cant get a factory one working,
The cars fitted with a MSD Pro Billet Dizzy, the tach lead from this is grey, am i right i thinking this connects to the tach signal input which is green?
Any body done this ??

Yup.

Grey wire isnt used. Or at least doesnt have to be. Green wire from the tach takes a feed straight from the -ve on coil. Doesnt go near dizzy - grey wire unconnected on mine. (cant remember why I did it this way, but there would have been a reason) Tach works !

grey wire is a square or saw tooth signal for electronic tachos and for driving rev limiters or FI or anything where you need electronics to talk to more complex electronics i.e its a special signal for stuff that understands it

if the tacho is original style, designed for retro fit to old cars it works off the back pulse in the coil primary, the effort of creating the spark in the secondary produces a similar pulse in the primary but smaller, hence useful for tacho.
This is a massive spiky signal off the coil negative in comparison to the conservative small voltage signal on the grey wire.
so you may find both of your tachos work just by plugging the green wire from the car loom into coil negative

so it very much depends on your new autometer gauge. if it wasn't purchased to work specifically with an ECU style signal it will most likley be one, like Morgan says...that works off the coil negative

there will be a wiring picture somewhere if you have a look based on model number

dave

Cheers guys, very helpful ............

Ah ha ! I knew there was a reason! And Dave knew what it was. Top effort. Actually, ‘Dave said’ is probably the reason I did it !!

Morgan i think I'm just relaying the outcome of your work...

dave