Ignition Switch Connector Fail

Have you, by any chance installed a new alternator recently? In my 1970 FSM the standard alternator output is 31 to 37 amps, A/C cars and Heavy Duty uses 41 to 47 amps, and for Fleet vehicles - cop cars, cabs, etc - 48-54 amps (for which Chrysler bypassed the bulkhead connector for that same wire you are having trouble with). These days you get a nice fancy looking alternator and it puts out 90-100 amps, if not more. Just try to get one that put out standard amperage for your 40-50 year old wires. I had to take an old one to a rebuild shop to get it down to 43 amps, after almost burning up my Dart through that circuit after I installed a shiny chrome alternator.