You need a test light or meter.
The Blower Mode switch has two contacts, one to turn on the Blower Relay and one to turn on the A/C compressor. When in any position but off the Blower Relay should be on. The Blower relay is connected to the Resistor Pack and then to the Blower Motor. The Blower Speed switch only bypasses part of the Resistor Pack to provive higher speeds than the low speed resistor.
Check for 12v starting at the Blower Mode switch, then the Resistor Pack, then the Blower Motor. If there is nothing on the Blower Mode switch, check the Ignition relay. If there is nothing on the Resistor Pack, check the Blower relay.
