[68C15]

that looks like a blower control module. it serves the same purpose as a resistor. the HVAC computer sends a pulse width modulated signal to turn on and off a solid state switch which in turn controls blower speed.

red is ign. power, black is ground, gray is control signal, purple is blower power while the black next to it is blower ground.

borrowed from hayhauler post; Check voltage on the Gray/Black wire at the blower control module, check for 8 volts on high blower speed and about 2 volts on low speed . If it is OK, check the B+ on the Red wire and ground. Before replacing the blower module, amp draw the blower motor. The blower motor should draw less than 15 amps running on the Black wire. If all this is good, then the blower module needs to be replaced

when replacing module you remove the heads of rivets and install new unit with screws in the other holes visible in picture. they do it that way as it's quicker on the assembly line than using screws.

I should add that this design of blower control has a shorter life span that a resistor and is a common failure item. the large transistor inside gets overheated and the molecular structure of the emitter blows in the same manner as a fuse. a new blower motor would be a good idea to prevent premature failure of new module.