Blower Motor Circuit Question

[JoePolo]

Reviving a 72 C10 that’s been dead since the 90s. It’s a factory AC truck.

Blower motor fuse/AC fuse (25A) is popping whenever the switch is turned on from the off position. I had a switch that worked from our Blazer so I pulled the connector and hooked it up out of the panel and blew the fuse again.
With the switch in the off position I have power to the input and I accidentally jumped it with the test light to the terminal just above and it actually kicked the blower motor on. So I know the motor isn’t stuck.

Resistor? God I hope not, I know they are deep in the box.
Relay? On the side of the box. I might have one of those I could test too.

My seat is out right now so trying to get anything that might be under dash figured out now.

Thanks guy.