Fuel Pump Relay

This procedure covers diagnosis and replacement of the fuel pump relay on a 1970 AMC Rebel Machine with 390ci V8 engine.

Warnings

Tools required

Parts

• Fuel pump relay × 1 — Standard automotive relay, verify amperage rating
• Dielectric grease × 1 — Use OEM specification

Preparation

1. Park vehicle on level surface and engage parking brake
2. Turn ignition to OFF position and remove key
3. Disconnect negative battery cable to prevent electrical shorts
4. Allow engine to cool completely if recently operated
5. Locate the fuel pump relay - typically found in engine compartment on firewall, inner fender, or in aftermarket relay panel if electric fuel pump was added
6. Verify vehicle actually has electric fuel pump relay before proceeding, as factory 1970 AMC 390 engines used mechanical fuel pumps

Procedure

1. 1

   Identify relay location and configuration
   Trace the fuel pump wiring from the electric fuel pump forward to locate the relay. On aftermarket installations, the relay is commonly mounted on the firewall or inner fender well. Note the relay orientation and wire colors connected to each terminal before removal. Take a photo if possible for reference during reinstallation.
2. 2

   Test relay operation
   Reconnect negative battery cable temporarily. Turn ignition to ON position (do not start engine). Listen for relay clicking sound and fuel pump activation. If relay clicks but pump doesn't run, problem may be elsewhere. If no click, relay is likely faulty. Use test light or multimeter to verify 12V power at relay power supply terminal. Turn ignition OFF and disconnect battery negative cable again.
   ⚠Do not crank engine during testing to avoid flooding or creating fuel vapor.
3. 3

   Remove relay from socket
   Pull relay straight out from socket or mounting bracket. If relay is hard-wired rather than plug-in type, disconnect individual wire terminals. Label each wire with tape indicating its terminal position on the relay (typically marked 30, 85, 86, 87, 87a).
4. 4

   Inspect relay socket and terminals
   Examine socket terminals for corrosion, burning, or loose connections. Clean terminals with wire brush or fine sandpaper if corrosion is present. Check for melted plastic indicating overheating. If socket is damaged, it must be replaced along with relay.
5. 5

   Bench test old relay
   Using multimeter set to continuity or resistance mode, test relay operation. Apply 12V across coil terminals (85 and 86) and verify continuity between common (30) and normally-open (87) terminals. If relay does not click and show continuity when energized, it is defective.
6. 6

   Install new relay
   Apply small amount of dielectric grease to relay terminal blades. Insert new relay into socket ensuring proper orientation matching photo or notes from step 1. If hard-wired type, reconnect wires to corresponding terminals: terminal 30 to battery power, 85 to ground, 86 to ignition-switched trigger, 87 to fuel pump positive. Ensure all connections are tight and secure.
7. 7

   Secure relay mounting
   Verify relay is fully seated in socket or mounting bracket. If relay uses separate mounting bracket, ensure bracket is securely fastened to firewall or fender and relay cannot vibrate loose during operation.

Reassembly

1. Reconnect negative battery cable
2. Verify all wire connections are secure and properly routed away from hot or moving components

Verification

• Turn ignition to ON position without starting engine - fuel pump should run for 2-3 seconds then stop, and relay should produce audible click
• Start engine and verify it runs normally with steady fuel pressure
• Turn engine off, wait 10 seconds, then restart to verify relay operates consistently
• Check for any fuel leaks around fuel pump and fuel lines
• If fuel pump does not activate, recheck all wire connections and verify relay is correct type and properly oriented

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