Where tack wire goes with orange box

[KENTON]

I just got a 3906 Autometer tach. I was wondering if you could wire it to the - side of the distributor, or if it has to go to the orange box?

 

[mopowers]

I've always just connected it directly to the (-) side of the coil.

 

[TrailBeast]

The distributor won't run the tach unless you have something like a built in HEI distributor and run it off the - coil terminal at the distributor.
Always best to go to the - of the coil on conventional ignition system, or at least somewhere along that same wire.

 

[KENTON]

OK thanks, the instructions said if you had an ignition box like a MSD don’t hook it to the coil. I wasn’t sure if the orange box would be the same.

 

[superchargeddrt]

Like it was already said, connect it to the negative side of the coil and you'll be ok.

 

[67Dart273]

OK thanks, the instructions said if you had an ignition box like a MSD don’t hook it to the coil. I wasn’t sure if the orange box would be the same.

MSD is capacitive discharge and works "sort of" like a photoflash. That is, when triggered, it dumps a hi voltage capacitor across the coil. Many people call more conventional systems "switched". Probably a better name is "Kettering." This includes breaker points, Mopar electronic, GM HEI conversions, the many "ready to run" imports, and Pertronix.

Everything except the MSD hooks to coil NEG just like old breaker points