The TOP wire on the coil is a vague description.Do you mean the HT output to the distributor cap.If you have current there, then you have current at the distributor cap plug lead connections unless the HT lead is faulty.If there is no current at the plug leads then you have either a rotor arm fault or a faulty distributor.If you mean that the top wire is the wire from the ignition (live feed to the coil ) but no spark coming out of the coil on the HT side and the LT wire to the distributor hasn't a break in it and your coil is working properly then your distributor is not switching the LT side on and off to produce the HT spark
