Welcome aboard Newb. Signal canceling is as stated above. The only thing I can add to your heater switch question is that it indeed would depend whether your hot wire is at a switched location or not. My 59 recirculating heater switch, the rotating one, was wired constantly hot therefore it would have to be manually switched off. Only problem I ever had is when I used the low speed and it was so quiet I left the truck only to return to a dead battery. Only took a time or two for me to always use medium or high speed.
