A shorted tach line (like the wiring you already checked and is good) or a shorted tach will pull the negative part of the coil to ground continuously and not allow the coil to fire. Mopar tachs are pretty simple with a couple of transistors and a few resistors. A shorted transistor (base to emitter short, ie) will shunt the points or electronic ignition signal to the coil to ground and not allow it to discharge to the secondary and allow a spark.
Craig