Blower wiring

[Badass70]

Im having this problem with the wiring to the blower for the heater, if I directly connect the blower to the battery it works fine but if you connect it to the stock wiring you get nothing. Not sure if it's bad connections at the plugs or what. Where should i start looking? Fuses are fine. Should I just run new wiring to the fan switch?

[stangg]

I'd check the blower motor resistor first ... Not sure about '70,  but they are typically mounted in the heater box.