I'm with John on this one. There are other possibilities for sure, but most likely it's the brown wire that goes to your ballast resistor. It wouldn't be the ballast itself since the brown wire bypasses the ballast. Trace the power on that wire back from the ballast, to the bulkhead disconnect, to the big plug (7-pin or so?) inside the car at the bottom of the steering column & finally back to the ignition switch....my 2-cents.

I REALLY like rapidroberts idea of pulling the yellow wire off of the ignition relay during your test. That would allow a friend of yours to hold the key in the start position while you run your tests & not have the starter spinning the whole time & burning up