74 duster heater wiring (non ac)

I am trying to learn about the heater wiring in my 74 duster. My blower motor will not turn on when switched to on. I have a good wiring diagram but it seems to be for an ac car. Are the parts different? Power comes from #2 fuse. It powered radio, blower motor, back up lights, and turn signal. My turn signals and reverse lights do work. I think my radio is bad. Where do I start to determine what is bad? Thanks guys