1973 Dart No electrical power

Think how old these girls are. Fuse links can maybe been pre-overheated and partially damaged in a previous event, or corroded. In fact I had a main battery cable on a Ranger corrode internally. The ground went from the battery down to a factory "T" terminal that bolted to the frame, then continued on to ground to the block. One day the Ranger would not crank, yet the headlights worked. Right after that "T" tap terminal, the cable was powder.

One way you can troubleshoot for shorts and guarantee you don't burn stuff up is to find an old heavy lamp, like a headlamp, or 1 or 2 stop/ tail lamps in parallel for more wattage. Put the device in series with the battery ground, and if the short appears, all it will do is light the lamp.