How does the ballast figure in? It should be bypassed/ removed.
The connection you are testing there has more load, normally that is, than just the ignition. It also junctions and feeds to the alternator field, the VR "ign" terminal, and possibly some underhood smog devices. EG electric choke, distributor retard, idle solenoid, and some other "junk."
IT MIGHT BE that your bulkhead connector is loose/ corroded and that you wiggled it just enough to "unmake" the poor connection. I'd start by pulling that apart and inspecting and repairing.
