Hello, thank you for asking about your 1974 Pontiac Ventura. From what you describe it appears to me that you are attempting to convert a points ignition system to an electronic HEI ignition system. This is a very common conversion...
Turning on one additional switch creating a loss of all power suggests you have a short somewhere in your system. The additional power draw that the extra fan is creating puts an additional load on voltage being supplied to other...
