When I bought my son's 71 Swinger, I stopped for gas after I bought it. Got gas, then nothing, no lights, no crank, nada. Had it towed home
and the next day my son moved the positive cable and power. This was 20 years ago and at that time new cable was available from the dealer.
I have a feeling the guy I bought it from had the same problem and that is why he sold it.