Harley Davidson Fuel Pump Not Coming On? Here’s How to Diagnose and Fix It

If your Harley Davidson's fuel pump doesn't turn on when you turn the ignition key or hit the kill switch, your motorcycle won't start or run. A silent fuel pump signifies an electrical or mechanical problem preventing it from receiving power or operating. Diagnosing this requires a methodical approach, starting with the simplest and most common causes before moving to more complex possibilities. This guide provides a practical, step-by-step process any Harley owner can follow.

Immediate Action: Basic Checks

1. Confirm the Problem: Listen carefully near the fuel tank when you first turn the ignition key or flip the run switch back to "Run" (after it was in "Off"). You should hear a distinct humming or buzzing sound lasting 1-5 seconds – the fuel pump priming. If you hear nothing, the pump isn't activating. Repeat this a couple of times.
2. Check Your Kill Switch: This is easy to overlook. Ensure the right-hand handlebar kill switch is firmly in the "Run" position (often marked with an icon or the word "Run"). A faulty kill switch or loose connection here can prevent the pump circuit from completing.
3. Verify Fuel: It sounds obvious, but check your fuel level. Most modern Harley-Davidson fuel pumps are submerged in fuel for cooling and lubrication. Running extremely low or completely out of fuel can cause premature pump failure. Ensure there's sufficient fuel in the tank.
4. Inspect the Battery: A weak or dead battery is a common culprit. Confirm the battery voltage is strong – it should read at least 12.4 volts at rest, and around 12.6V or higher is better. Significant voltage drop when turning the ignition can prevent the pump relay from engaging. Check battery terminals for tightness and cleanliness. Corrosion creates resistance. A failing battery, even if it shows decent voltage unloaded, can fail under the pump's initial power demand.
5. Check Main Fuses: Locate your main fuse box. On most Harleys, this is found under the seat. Refer to your owner's manual or a service manual for the exact location and diagram for your model. The fuel pump typically has its own dedicated fuse, often labeled "FP," "Fuel Pump," "EFI," or similar (e.g., a 10A, 15A, or 20A mini blade fuse). Look for the "Ignition" or "ACC" fuse as well, as power for the pump relay usually flows through this first.
   • Remove each relevant fuse visually.
   • Look for a broken element inside the clear plastic housing or signs of melting/charring.
   • Test them with a multimeter set to continuity. Replace any blown fuses immediately with the correct amperage rating.
   • Important: If a fuse blows again immediately after replacement, DO NOT keep replacing it. You have a significant short circuit downstream that needs diagnosis. Continuing risks wire or component damage or fire.

Step 1: Diagnosing the Fuel Pump Relay

The fuel pump relay (often referred to as the FP relay, ECM relay, or accessory relay) is the switch controlled by the ECM that sends main battery power to the fuel pump. It's a very common failure point and a primary suspect.

1. Locate the Relay: Relays are usually found under the seat, near the fuse box, or sometimes under the tank. Identify the relay dedicated to the fuel pump; consulting a wiring diagram specific to your model and year is crucial. Common relay types include the black "ISO Micro Relay" or a silver canister type.
2. Swap Test: The easiest test is often swapping the suspect fuel pump relay with another identical relay in your fuse box (like the horn relay or headlight relay, ensuring they share the same part number).
   • Warning: Never swap relays of different amperage ratings or terminal configurations (pinouts).
   • Swap relays.
   • Turn on the ignition and listen for the pump priming sound.
   • If the pump now works, the original fuel pump relay is faulty. Replace it.
3. Relay Click Test: With the ignition OFF:
   • Pull out the fuel pump relay.
   • Insert the probes of your multimeter (set to DC Volts, 20V scale) into socket cavities corresponding to relay terminals 85 and 86 (these are the control coil terminals). Refer to your service manual or a relay diagram (often printed on the relay itself) to identify which socket terminals are which.
   • Turn the ignition key ON. You should see battery voltage (typically 12V) appear on terminals 85 or 86. One of these terminals usually goes to switched power (from the kill switch circuit), the other goes to ground via the ECM. The ECM provides the ground path to activate the relay coil when it wants the pump to run.
   • No Voltage? Problem lies upstream in the ignition/kill switch circuit feeding the relay control side.
   • Voltage Present? Reinsert the relay carefully. With the ignition ON, you should hear and feel a distinct "click" from the relay. If you don't hear a click, the relay's internal coil is likely faulty, or it's not getting a solid ground path from the ECM (more on ECM later).
4. Relay Output Power Test: Test for power coming out of the relay on its main power output terminal (often terminal 87 or 30) heading to the pump:
   • Set multimeter to DC Volts (20V scale).
   • Place the multimeter's negative probe on a solid ground (battery negative terminal is best).
   • Carefully backprobe the wire going to the pump on the relay socket terminal (terminal 87 or 30 - check diagram) while the ignition is ON.
   • You should see battery voltage (approx. 12V+). If you have voltage here but the pump still doesn't run, the problem is between the relay socket and the pump (wiring/harness damage, pump connector, or the pump itself).
   • No Voltage at Terminal 87? Either the relay itself is faulty (power not passing through its contacts), terminal 30 isn't getting constant battery power (check main fuse and wiring), or the relay control circuit (coil) isn't activating.

Step 2: The ECM Connection - Ground Control

The ECM provides the critical ground signal that completes the circuit to activate the fuel pump relay's control coil (terminal 86 usually).

1. Testing ECM Ground Signal: Requires a helper:
   • Set multimeter to DC Volts (20V scale). Place the black (negative) probe on the battery negative terminal.
   • Place the red (positive) probe back on terminal 86 of the relay socket.
   • Have a helper turn the ignition key ON while you watch the meter.
   • Momentarily, when the ignition is turned on, the meter should drop from showing 12V (or whatever voltage was present earlier on terminal 86) down to near 0 volts. This signifies the ECM has provided a ground path, completing the relay coil circuit.
   • What if the voltage doesn't drop? This strongly suggests a problem with the ECM ground control for the pump relay. Causes include:
     • Bad ground connection at the ECM itself (check ECM grounds).
     • Faulty wiring between the relay and the ECM (harness damage).
     • A problem with the ECM itself not sending the ground signal.
     • An immobilizer/fault code preventing ECM operation (check diagnostic mode).
     • Tip: Check for Diagnostic Trouble Codes (DTCs) using your Harley's built-in diagnostic mode (process varies by year/model).

Step 3: Wiring and Harness Inspection

Between the relay and the pump itself, the wiring can be vulnerable to damage. Look for:

1. Pinched or Chafed Wires: Especially where wiring runs near the frame, steering head, triple trees, or under the tank. Vibration and movement can cause abrasion over time.
2. Corroded or Loose Connectors: Inspect the connector at the fuel pump itself under the fuel tank flange. Carefully disconnect it and examine the terminals for corrosion (green/white powder), bent pins, or signs of heat damage/melting. Also check the relay socket terminals for tightness and corrosion.
3. Vibration Damage: Harley engines vibrate significantly. Wire strands can break inside insulation near connectors or stress points, leading to intermittent or complete failure.
4. Rodent Damage: Check for any signs of chewing on wires, especially if the bike has been stored.

Testing Pump Circuit Continuity and Voltage:

1. At the Pump Connector (Harness Side) Test for Power and Ground:
   • CAUTION: Fuel vapor is present. Ensure area is well-ventilated. No sparks! Locate the fuel pump connector underneath the fuel tank mounting flange (you will need to raise or remove the tank).
   • Set multimeter to DC Volts (20V scale).
   • Place the black probe on a known good ground (frame bolt, engine case, battery negative). Place the red probe on the terminal in the harness side connector that corresponds to the fuel pump positive (+) wire (consult wiring diagram for color code - common is orange/white).
   • Have a helper turn the ignition ON. You should see a brief surge of battery voltage for the prime cycle.
   • If voltage is present: The wiring and relay circuit to the pump is good. The problem is the pump itself (or possibly the ground connection to the pump - test next).
   • If voltage is absent: The problem remains in the relay circuit or wiring upstream.
2. Test Ground Circuit at Pump Connector:
   • Place the multimeter's red probe on the battery positive (+) terminal.
   • Place the black probe on the terminal in the harness side connector that corresponds to the fuel pump ground (-) wire (common is black).
   • Set multimeter to DC Volts (20V scale).
   • The reading should be approximately zero volts. If you see any significant voltage (e.g., more than 0.5V), there is high resistance in the ground path back to the battery - find and clean that ground connection.
3. Continuity Check Pump Ground Path (Power OFF):
   • Set multimeter to Ohms (Ω) setting.
   • Place one probe on the ground terminal (harness side) of the fuel pump connector.
   • Place the other probe on the battery negative (-) terminal.
   • You should see very low resistance, typically near 0 Ohms. Any significant reading (e.g., over 1 Ohm) indicates a poor ground connection. Trace and clean the ground path.

Step 4: Testing the Fuel Pump Itself

If voltage and ground are both confirmed good at the pump connector during prime, yet the pump doesn't run, the pump assembly itself is almost certainly faulty.

1. Direct Power Test (Requires Removing Fuel Pump from Tank):
   • CRITICAL SAFETY WARNING: Fuel pumps can spark internally. Performing this test on an open pump assembly near fuel vapor is EXTREMELY DANGEROUS and risks fire or explosion. Only perform this test with the pump assembly completely removed from the fuel tank and away from any fuel sources or vapors.
   • Remove the fuel pump module from the gas tank (refer to service manual).
   • Ensure the pump body and wiring are dry and away from fuel/vapors.
   • Identify the two pump motor terminals (usually two spades/lugs on the pump itself).
   • Connect jumper wires: Attach one wire from the battery POSITIVE (+) terminal to the pump POSITIVE (+) terminal (consult diagram/pump labeling).
   • Momentarily (less than 1 second!) touch the other jumper wire from the battery NEGATIVE (-) terminal to the pump's NEGATIVE (-) terminal.
   • Warning: Do not connect the pump for more than a second or two when dry, as lack of fuel can quickly damage it.
   • What Happens?
     • Pump Runs: It was functional during this test. This does not guarantee it works perfectly under load/pressure in the tank. If the wiring circuit is good but it doesn't run in the bike, suspect wiring/connectors outside the tank, or an intermittent fault within the pump module itself (less common).
     • Pump Doesn't Run or Struggles: The pump motor is confirmed dead or dying. Replacement is required. Signs include buzzing, humming but no movement, or simply doing nothing.

Step 5: Fuel Pressure Test - Confirming the Symptom's Cause

While your symptom is a silent pump, a fuel pressure test confirms if the issue actually prevents fuel delivery and verifies the problem wasn't a running pump that failed internally without failing electrically.

1. Purpose: To verify fuel pressure reaching the required specification for your engine (usually 50-55 PSI for EFI Harleys, potentially higher for M8s under high flow conditions).
2. Method: Requires a suitable fuel pressure tester gauge kit that adapts to your bike's fuel injector rail test port (common on Sportsters and Dynas) or connects inline between the pump outlet and the main fuel line (often required for Softails/Touring models).
3. Test:
   • Connect the tester following kit instructions.
   • Turn ignition ON to prime the pump.
   • Observe the pressure reading on the gauge.
   • Expected Outcome: Pressure should briefly spike to the expected PSI value during prime and hold that pressure for many minutes if the pump and injectors are healthy. If the pump was electrically functional but mechanically dead, you would get 0 PSI. If the pump is weak, pressure might build slowly or not reach spec.

Replacement and Installation Tips

Once you've diagnosed a faulty pump assembly, replacement involves:

1. Obtaining the Correct Part: Use your VIN at a dealer or reputable parts supplier to ensure compatibility. Beware of cheap, low-quality pumps.
2. Draining Fuel: Siphon or drain most fuel from the tank before removal. Protect painted surfaces from spills.
3. Remove Tank: Disconnect fuel lines (carefully relieving any pressure if possible), electrical connectors, and vent lines. Support tank safely.
4. Accessing the Pump Module: Remove the lockring securing the pump module to the tank. Some models require a special spanner wrench tool. Tapping gently around the ring perimeter with a blunt punch can loosen it if stuck. Avoid twisting the assembly.
5. Replacement Steps:
   • Lift the module straight out. Note the orientation for reassembly.
   • Replace necessary components. Often, replacing the entire module (housing, pump, filter, sender) is the most reliable fix. Rebuilding kits (just the pump element) exist but require careful work and may not last.
   • Replace the fuel filter sock on the bottom and all rubber O-rings/seals. Inspect the tank interior for debris/contamination and clean if necessary.
   • Ensure all electrical connectors inside the module are fully seated.
   • Reinstall the assembly carefully. Align correctly and tighten the lockring firmly and evenly.
6. Reinstall Tank: Connect all hoses and electrical plugs correctly. Double-check connections.
7. Initial Power-Up: Turn ignition ON and listen for the healthy prime sound. Check for leaks immediately. If priming sounds abnormal or leaks are present, turn off ignition and recheck your work.

Preventative Maintenance Tips

1. Keep Fuel Levels Up: Avoid running the tank below 1/4 full habitually. Low fuel levels starve the pump for cooling/lubrication and accelerate wear.
2. Avoid Old Gas: Stale gasoline can varnish and gum up pump internals. Use fuel stabilizer if storing for more than a few weeks. Don't store the bike with a full tank indefinitely; run treated fuel through it periodically or drain it.
3. Monitor Electrical Components: Periodically check battery terminals and main ground connections for tightness and corrosion. Inspect fuses visually. If the relay is old or you've had a fuse blow, consider proactively replacing the fuel pump relay.
4. Consider Upgraded Relay: Harley's OEM ISO Micro relay (often part number 70450-08) can be replaced with a higher-quality unit like a Bosch or Tyco relay (available from automotive suppliers). Ensure the pinout matches exactly.

Conclusion

A Harley Davidson with a fuel pump not coming on leaves you stranded. By systematically checking through the points outlined – basic controls, fuses, battery, fuel pump relay, ECM ground control, wiring harness integrity, and finally the pump itself – you can reliably identify the root cause. Start simple and work logically towards the pump. Don't skip steps. Safety, especially concerning fuel vapor and sparks, is paramount during any testing involving the pump circuit. Once diagnosed, replacing the faulty component – whether a fuse, relay, or the entire pump module – will restore the essential fuel delivery your Harley needs to roar back to life. Regular attention to fuel levels, battery maintenance, and clean electrical connections helps prevent future occurrences.