[Titomars]

you could go with a vacuum switch at the dash and use a standard vacuum valve in the heater hose line. I used to use a 64 to 66 Thunderbird vac switch for the rear defrost to do all sorts of things on various cars. I mostly used them for powerglide equipped street/strip cars. I used them for switching off and on the vacuum modulator. On street, off race. I might go this route for my own truck.