Blower Motor doesn't shut off.

I was trying to figure out why my blower motor wasn't working. Opened the hood and found it wasn't plugged in. Figured the previous owner just forgot to plug it back in. So plugged it back in and turned the key on, and found that it wouldn't shut off and it wouldn't change speed with the switch. So now I know why it wasn't plugged in, in the first place. So is this just a wiring issue, previous owner got their wires crossed, or is this common and some place I should start looking? This is in my 1976 Duster by the way.