I did a quick search so I wouldn't have to bother anyone with this but I didn't find anything that jumped out at me. It's a 1966 chevelle with heat only. I have the heater core completely out and I notice that there is a space on top of the box for a two or three prong switch of some sort but there is nothing there. I also had an old heater core from another 66 that has the same thing and I thought I remembered there being something there but when I looked closer there is nothing, yet it seems like my wiring harness is looking for something over on that side to plug into. What is it and do I need it? I haven't had the blower motor working or found any wire that has power to it when the control box is turned to fan/on with the ignition in the on position.

this space is where the blower resistor goes. it is basically two or three coils of different size wire that create different levels of resistance between the blower switch and the wire that feeds the blower. high blow is just a straight shot through the resistor board or through a blower relay. hope you understand

absolutely, thanks