I had the ignition feed wire do the same thing and it was due to the poor, original wire just breaking down at the bulkhead.
I cut the wire on both sides of the bulkhead and made a new wire and rerouted it thru the firewall grommet in front of the pedals.


1970 YO7 A66 [Canadian Export] F8 Challenger
340 (Currently in shop for stroker assy.)