Got a crazy Starting Issue! ........I mean nutz!

Years ago I was a weapons mech on USAF fighter A/C We had an aircraft (F102) that would run through the missile firing sequence with no one in the aircraft and with the stick grip trigger in our hand(s). It was some what unnerving! The problem was exactly what you are describing, in the aircraft's case it was a short between the firing circuit pin and the ground pin. I'll bet your problem is at the bulkhead with shorted wires.