Why does the HVAC fan motor keep running sometimes after the engine is shut off?

the radio may have its wiring tapped into the wrong pwr lead, take it back and havethem ck there work

This is normal. If you have run the A/C while driving, the heater fan will turn on after the car is shut off to help remove moisture from the A/C Evaporator. Allowing the moisture to remain can cause bacteria growth, which is why A/C systems can smell funny at times. You may see this referenced in your owners manual, but I'm not positive.