Short under the dash.

These two are good if you feel stuck or lost on trouble shooting.
1973 Chrysler and Imperial Understanding The Electrical System Service Reference Guide from the Master Technician Service Conference Series Session 310

1973 Chrysler and Imperial Electrical Circuit Troubleshooting from the Master Technician Service Conference Series Session 311

Below is are couple functional diagrams which may help visualize the relationships.

Main_charging_wires_pluss.png

Main_charging_wires_plus-off.png