86 gmc C1500 Blower motor won’t turn on?

[Billys44s]

So I’m having an issue with my blower motor, I just bought a new one a few weeks back and it worked for the 1st few days but it suddenly stop powering on, so I decided to do some digging and if I hook a wire straight up to power it comes on but if I use the fan controls inside the cab, nothing happens, I Checked the main power wire going to the plug and it gets 12 volts while the switch is on but the blower motor still doesn’t do anything

 

[CheemsK1500]

Edit: misread post. I'd suggest removing the HVAC switch from your dash, and tracing the wires.

I once had a bullnose Ford pickup that had this same problem. It ended up being the ignition switch on the steering column. On many vehicles, most of the key-on devices power (such as the blower motor) originates from the ignition switch.

 

[Arizona Ranger K5]

There is a "heater fan relay" on the outside of the a/c box (on my '81) and there is also a "heater fan resistor" in the top of the a/c box. heater fan resister I believe controls speed setting, relay controls operation of fan. I have to change out both of mine.