Honda Rancher 420 Fuel Pump Relay Replacement: A Complete Guide

If your Honda Rancher 420 is having trouble starting, stalling, or losing power, the fuel pump relay is one of the first components to check before replacing the fuel pump itself. The fuel pump relay on a Honda Rancher 420 is located in the fuse/relay box under the seat on the left side near the battery, and it is a standard 5‑pin relay labeled "FUEL PUMP" in most fuel‑injected models. Replacing a faulty relay is a straightforward, low‑cost fix that can save you from unnecessary fuel pump replacement. This guide walks you through locating, testing, and replacing the relay, along with diagnosing common fuel delivery issues.

Where Is the Fuel Pump Relay Located?

The Rancher 420's electrical box is typically tucked behind the left‑side panel beneath the seat. To access it, you need to remove the seat and the left panel to reveal the main fuse/relay block where the fuel pump relay sits alongside other relays and fuses.

Steps to access the relay:

  1. Remove the seat by lifting the latch to unlock the seat panel.
  2. Open the left‑side panel to expose the fuse/relay box.
  3. Identify the fuel pump relay—usually a 5‑pin unit labeled "FUEL PUMP" near the ECU and other relays.
  4. Carefully disconnect the wiring harness connector from the relay if you need to test or swap it.

In most fuel‑injected 420 models, the left‑side under‑seat fuse block is the standard location. Carbureted variants may differ or lack a dedicated fuel pump relay. Some owners report that behind the battery, under the fuse box, there are three relays, and the fuel pump relay is often the one at the very bottom, positioned at an angle under the fuse box.

How to Test the Fuel Pump Relay

Before replacing the relay, perform a few basic tests to confirm it is the actual problem. These tests also help rule out other issues like a blown fuse, a bad fuel pump, or a clogged filter.

1. Listen for the prime sound. With the ATV parked and the engine off, turn the ignition key to the "ON" position without cranking the engine. Listen near the fuel tank for a short whirring sound lasting about two to three seconds. This indicates the fuel pump is priming. If you hear nothing, proceed to check the electrical components.

2. Check the fuses and relay. Locate the fuse box (under the seat or near the battery). Find the fuse labeled "Fuel Pump" or "FI" (Fuel Injection). Remove the fuse and inspect it for a broken wire. If the fuse looks intact, use a multimeter to test for continuity. Also, swap the fuel pump relay with a known‑good relay of the same type to see if the pump starts working.

3. Check for voltage at the pump connector. Use a multimeter to test the electrical connector at the top of the fuel pump assembly. With the ignition in the "ON" position, you should see 12 volts at the connector. If you have voltage but the pump does not run, the pump motor is dead. If you have no voltage, the problem is upstream in the wiring, relay, or ECU.

4. Measure fuel pressure. For a more accurate diagnosis, connect a fuel pressure gauge to the fuel rail service port or tee into the fuel line between the pump and the engine. Honda Rancher 420 EFI systems typically require between 40 and 50 PSI. If the pressure is low, inconsistent, or zero, the fuel pump is likely faulty.

Common Symptoms of a Bad Fuel Pump Relay

These signs often point to a failing relay, though they can also come from upstream issues such as wiring or fuel delivery components:

  • Difficulty starting or a complete no‑start condition
  • Engine stalling or sputtering under load
  • Long crank times before the engine fires up
  • Poor acceleration or loss of power at high RPMs
  • No fuel pump prime sound when the key is turned on

Some owners report intermittent problems where the ATV runs fine for a while, then suddenly won't restart until it sits for 30 minutes. This is a classic sign of a failing relay or fuel pump.

Step-by-Step Replacement Guide

Replacing the fuel pump relay is a simple task that requires basic tools and about 15 minutes.

Step 1: Purchase a replacement relay. The OEM replacement relay typically costs around $30 to $40. Look for a proper Honda OEM or equivalent 5‑pin relay. OEM part numbers 38580‑HP5‑601 and 38580‑HP5‑600 are the genuine Honda replacement numbers. This relay is a standard 15A x2 waterproof unit that fits many Honda ATV models, including the TRX 420 Rancher (2007-2014), TRX 500 Fourtrax (2012-2013), and TRX 680 Rincon (2008-2018).

Step 2: Locate the relay. As described above, the relay is under the seat on the left side near the battery. Look behind the battery in the fuse/relay box.

Step 3: Clean and inspect. Before replacing the relay, clean the fuel pump relay prongs with a wire brush to remove any dust, rust, or corrosion. You can also use an electrical cleaner and a blower to ensure a thorough cleaning. Additionally, inspect the relay for any visible damage, such as cracked solder joints or blown fuses.

Step 4: Replace the relay. Simply remove the old relay by disconnecting it from the fuse box and install the new relay in its place, ensuring it is securely connected.

Step 5: Test the replacement. After replacing the relay, turn on the ignition and listen for the familiar clicking sound from the fuel relay. If the relay is functioning correctly, you should hear this sound. Additionally, start the engine and pay attention to whether your ATV stalls or has any issues starting.

Important Notes on Model Year Variations

Some early Rancher 420 variants or non‑FI versions may have different electrical layouts. Always consult the specific year manual or service guide to confirm the exact location and component labeling. For example, the 2010 Rancher 420 has the engine stop and fuel pump relay combined into one relay unit. The 2007 model may have a different setup, and a flashing FI light can indicate specific error codes that need to be looked up in the service manual.

Recommended Fuel Pump Upgrade: KEMSO

If you have already replaced the relay and still experience fuel delivery issues, the problem may be the fuel pump itself. When it comes to replacing the fuel pump on your Honda Rancher 420, KEMSO offers a high-performance solution that stands out from the competition.

KEMSO fuel pumps are designed as direct OEM replacements, meaning they fit perfectly without modifications. Each pump is built with high-quality components to ensure reliable performance and long service life. KEMSO backs every fuel pump with a lifetime warranty, giving you peace of mind that your investment is protected. Whether you ride on trails, work on the farm, or explore off-road terrain, KEMSO fuel pumps deliver consistent fuel pressure and flow to keep your engine running smoothly.

Visit KEMSO’s website at https://www.kemsoracing.com/ to browse their full selection of fuel pumps for Honda ATVs and other vehicles.

Conclusion

Replacing the fuel pump relay on your Honda Rancher 420 is a simple, low-cost fix that can resolve many common starting and performance issues. The relay is located under the seat in the fuse/relay box on the left side near the battery. Testing takes just a few minutes, and if the relay is faulty, a replacement is easy to install. If the relay checks out but problems persist, the fuel pump itself may need replacement. For a reliable, long-lasting fuel pump upgrade, consider KEMSO’s products, backed by a lifetime warranty. Visit https://www.kemsoracing.com/ for more details.


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