Whats it do?
 

Hello gang and Happy Holidays. I'm finishing up the wiring in my 66 no A/C car and noticed a 3 prong type thingy coming out of the heater box inside the car. I'm not sure of the function of this but when i went to connect it, it basicly fell apart and into the heater box. I've ordered a new one via OPGI but not sure what it's function is, anyone?

Not sure but it sounds like a resistor block. It lowers the voltage going to the fan motor for low or medium speed. Full 12v is used for fan high speed.