Blower motor has full power when the switch is set to HI.

There is a heater fan relay. The coil of the relay is fed by the 10A GAUGE fuse. It's energized when the blower switch is set to anything but OFF.

The switch part of the relay is between the 100A ALT fuse and the 40A HEATER fuse. So, you should see voltage on one side of the HEATER fuse when the blower switch is on. If the ALT fuse was melted, your day would have been much worse..

Also the blower motor should have two wires on the 97 truck (there are wire colors marked on both legs).. one leg comes thru the HEATER fuse, and the other leg gets ground from the heater switch (on HI) or the blower resistors (on other speeds.)

The heater relay also supplies power to the A/C fuse (and A/C brain.) If your blower switch is on, the A/C LED should light up when you push the button in.