What plugs here?

I have a 72 340 duster...I can't get my heater blower to come on, but I know it works because I tested it.. I found this hot wire under the dash but I dont know exactly plugs into it.. it is by the steering wheel.. I put a 7 amp fuse in it to see what would happen and my blower motor came on and stayed on and I could not control it with the switch,, my dash lights also came on .. so now that i know that this hot plug has something to do with the dash and blower motor, i need to find out exactly what plugs into it.. I was thinking some sort of relay or something,, but does anyone know exactly? its a two prong plug with 4 wires coming out the back of it