If it uses a magnetic pickup, check the gap, and that the shaft is rotating when cranking the engine.
Also, check for a short on the coils "-" side. It sounds like the coil is grounded on the "-" terminal, either a short, or the ignition module. When you turn off power to the coil, the magnetic field discharges into the secondary creating a single spark. Most of the electronic ignition systems will grounf the coil "-" terminal until it senses the trigger, so if the pertronix unit does not sense the rotation of the distribitor it will not release the grounded output which would normally create a spark. It is also possable the ignition coil has an internal short.