Cooling Fan Relay

Replace or install the cooling fan relay to restore proper operation of the electric cooling fan circuit on the 1970 AMC Rebel Machine with 390ci V8 engine.

Warnings

Tools required

Parts

• Cooling fan relay × 1 — Use OEM specification or equivalent 30A SPDT automotive relay
• Dielectric grease × 1 — Optional for terminal protection

Preparation

1. Park vehicle on level surface and engage parking brake
2. Allow engine to cool completely if recently operated
3. Disconnect negative battery cable to prevent electrical shorts
4. Locate the cooling fan relay, typically mounted on the firewall, inner fender, or near the radiator support

Procedure

1. 1

   Locate the cooling fan relay
   Identify the cooling fan relay in the engine compartment. On vehicles with aftermarket electric fan installations, the relay is commonly mounted on the driver side firewall, inner fender well, or radiator support bracket. The relay will have 4 or 5 terminals with wiring connected to the fan motor, ignition switch circuit, temperature switch, and ground.
2. 2

   Document wire connections
   Before disconnecting any wires, carefully note or photograph the wire routing and terminal positions on the existing relay. Mark each wire with tape and numbering (1-4 or 1-5) to ensure correct reinstallation. Common terminals include: 85 and 86 for coil control, 30 for battery power input, and 87 for fan motor output.
3. 3

   Remove relay mounting hardware
   Remove the mounting screws or bracket holding the relay in place. Most relays are secured with one or two screws or may be mounted in a relay socket bracket. Use appropriate screwdriver or socket to remove fasteners and set aside.
4. 4

   Disconnect electrical connections
   Carefully disconnect all wire terminals from the relay. If using spade terminals, pull straight off to avoid bending. If relay is socket-mounted, simply pull the relay straight out of the socket. Inspect all terminals and wiring for corrosion, heat damage, or loose connections.
5. 5

   Clean terminal connections
   Use wire brush or electrical contact cleaner to clean all wire terminals and socket contacts if applicable. Remove any corrosion or oxidation to ensure good electrical contact. Inspect wiring insulation for damage near terminals and repair as needed.
6. 6

   Install new relay
   Position the new cooling fan relay in the mounting location. If using a socket-type relay, align pins and push firmly into socket until fully seated. For direct-wired relays, prepare for terminal connection by applying a small amount of dielectric grease to each terminal if desired for corrosion protection.
7. 7

   Connect electrical terminals
   Reconnect all wire terminals to the new relay in the exact configuration documented in step 2. Ensure each spade terminal is fully seated and makes solid contact. Verify connections: terminal 85/86 to control circuit (temperature switch and ground), terminal 30 to switched 12V power source, and terminal 87 to cooling fan positive wire.
8. 8

   Secure relay mounting
   Install and tighten the relay mounting screws or brackets to secure the relay firmly in position. Ensure the relay is mounted away from excessive heat sources and moving components. Route any excess wiring away from belts, pulleys, and hot exhaust components.

Reassembly

1. Reconnect negative battery cable
2. Ensure all tools and materials are removed from engine compartment
3. Verify all electrical connections are secure and properly insulated

Verification

• Start the engine and allow it to reach operating temperature while monitoring the cooling fan operation
• The electric cooling fan should activate when coolant temperature reaches the thermostat or temperature switch set point (typically 180-195°F)
• Listen for relay clicking sound when fan engages, indicating proper relay function
• Verify fan turns off when temperature drops below threshold or engine is shut off
• Check for proper amperage draw with multimeter if available (typical draw 10-15 amps for aftermarket fans)
• Inspect all connections for signs of overheating or arcing after initial test cycle

More procedures for this vehicle