Mopar Orange Box with Tach

[bobscuda67]

I've been having a continuing problem with my ignition. It turns over but no start ever once in a while. I swapped out my FBO box to my Mopar orange and while it hasn't had a no start, it makes my tach needle bounce around at 2500. It works fine from idle to 2500 rpm. With the FBO box it worked like it's supposed to.
Anyone have the same issues? How did you fix it?

 

[KitCarlson]

The first thing to test is the the voltage at the + terminal of the coil to ground. With the engine running at idle and just above 2500 RPM. The ballast drops the voltage at that point, it will be typically about 7V. The charge time of the coil is directly related to the supply voltage. At low engine speeds, the available dwell time is long, as RPM increases, the available dwell time decreases, and the coil is not getting charged enough for proper ignition.

If my hunch is correct, there will only be 3 or 4V. If the voltage is correct then measure voltage from engine ground to chassis, it should be near zero. The root cause may be a poor connection at bulkhead connector, or engine to firewall ground.