Originally Posted by
Andy 2
If the fuse for the heater is good and there is power at the fuse, then it could be the switch or the resistors or the wiring.The blower switch is on the back of the panel that the heater controls are on. I would check the power cable and blower resistors first before taking the dash apart. They are located on the bottom of the blower next to the firewall. The plug from the switch plugs in to the resistor plate. Unplug it and use a test light to see if there is power there when you turn the blower switch on(be sure to have the ignition key on). Clamp the ground from the test light to the cab of the truck somewhere and check each tab of the plug on each blower setting. Each setting of the switch should power the plug in some way. If there is power, your switch is working.
The blower resistors are easy to check. Take out the 2 screws holding the resistor plate in and take it out of the blower housing. The resistor wires are delicate so be careful not to let them touch anything when you take them out. If the three small spring-like wires are intact, then the resistors are okay. You can check them with an ohm meter to be sure. All the mounts for the blower are plastic so that ground wire Lush90 mentioned is important.
If you have no power at the plug on any of the 4 speed settings then it could be your switch, the wires feeding it, or the wires coming from it that are faulty. The heater control panel is fastened to the dash behind the trim panel. If you're going to get in to removing the heater control, take care not to force any of the plastic parts as they will crack easily if they are cold.