63 Dart tachomoter

[Dartnewbie]

How would I add a tach to a /6 225 with electronic ignition? It will be an after market tach. Do I attach to the negative side of the coil or is there another spot to pick up the output?

 

[waggin]

green wire is the trigger,hook to negative side of the coil,red is a keyed hot(comes on with the ignition) white goes to the fusebox for instrument lamps(it will dim with the switch for the lights) and black goes to ground.