If the blower motor doesn't work, disconnect its electrical connector and use a test light between the harness connector terminals. If the test light glows, the power and ground circuits are fine, and the motor should be replaced. If not, identify the power and ground terminals. Connect the test light to a good chassis ground and probe the power terminal. If the light doesn't illuminate, check the fuse, relay, and wiring. If it does, check the ground circuit's continuity. If the motor works at some speeds, disconnect the blower resistor's electrical connector and check for continuity. If any resistor is open, replace the assembly. If the resistors are fine, remove the control panel and check for continuity in the blower switch and wires. Check for continuity to chassis ground at the blower switch harness connector ground wire. To replace the blower motor resistor, disconnect the electrical connector and remove the screws. To replace the motor, remove the lower dash panel and glovebox, disconnect the connectors, detach the wiring harness, and remove the motor. Installation is the reverse of removal.