Blower Motor Resistor

This procedure covers the replacement of the blower motor resistor, which controls the heater/ventilation fan speeds on the 1972 Ford F-100.

Warnings

Tools required

Parts

• Blower motor resistor × 1 — Use OEM specification

Preparation

1. Park the vehicle on level ground and set the parking brake
2. Turn the ignition to OFF and remove the key
3. Turn the heater blower switch to the OFF position
4. Allow the engine and heater components to cool if recently operated

Procedure

1. 1

   Locate the blower motor resistor
   Open the hood and locate the blower motor mounted on the engine side of the passenger-side firewall. The resistor assembly is mounted on or near the blower motor housing with the wire harness connector visible. On the 1972 F-100, the resistor is typically positioned near the blower motor and is most easily accessed from the engine bay.
2. 2

   Disconnect the wire harness
   Locate the multi-wire connector attached to the blower motor resistor. Grasp the connector body and pull it straight off the resistor terminal block. If the connector is difficult to remove due to corrosion or age, gently wiggle it side to side while pulling. Do not pull on the wires themselves.
3. 3

   Remove the resistor mounting screws
   Using a 5/16 inch socket and 1/4 inch ratchet, remove the mounting screws (typically 2) that secure the blower motor resistor to the blower motor housing. These screws thread directly into the metal housing. Keep the screws in a safe location for reinstallation.
4. 4

   Extract the resistor assembly
   Carefully pull the blower motor resistor assembly straight out from the blower motor housing. The resistor may have a rubber seal or grommet around it to prevent air leaks. Note the orientation and position of any sealing components for proper reinstallation.
5. 5

   Inspect the blower motor housing
   Examine the opening in the blower motor housing where the resistor was mounted. Look for signs of overheating, melted plastic, burned areas, or debris. If damage is present, the blower motor housing may need attention before installing the new resistor. Check that the mounting screw holes are intact and not stripped.
6. 6

   Install the new resistor assembly
   Position any rubber seal or grommet onto the new resistor assembly in the same orientation as the original. Insert the new blower motor resistor into the opening in the blower motor housing, ensuring the mounting screw holes align properly and the resistor sits flush against the housing.
7. 7

   Secure the resistor with mounting screws
   Thread the 2 mounting screws through the resistor flange and into the blower motor housing. Tighten the screws snugly with the 5/16 inch socket and ratchet, ensuring the resistor is firmly seated but being careful not to over-tighten and crack the resistor housing or strip the mounting holes. Hand-tight plus a quarter turn is sufficient.
8. 8

   Reconnect the wire harness
   Align the wire harness connector with the terminal block on the new blower motor resistor. Push the connector firmly onto the terminals until fully seated. Verify the connector is snug and the terminals are fully engaged.

Reassembly

1. No disassembly of other components was required for this procedure

Verification

• Turn the ignition key to the ON position without starting the engine
• Test all blower motor speed settings (LOW, MEDIUM-LOW, MEDIUM-HIGH, HIGH) to verify each speed operates correctly
• Listen for consistent fan operation at each speed with no unusual noises or hesitation
• Verify that the blower motor stops completely when the switch is turned to OFF
• Check that the resistor assembly is not producing any burning smell during operation
• Confirm that the wire harness connector remains securely attached during blower operation

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