Honda Rancher 420 Fuel Pump Relay: Location, Testing, and Replacement Guide
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. It is a standard 5‑pin relay labeled "FUEL PUMP" in most fuel‑injected models. If your 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. 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:
- Remove the seat by lifting the latch to unlock the seat panel.
- Open the left‑side panel to expose the fuse/relay box.
- Identify the fuel pump relay—usually a 5‑pin unit labeled "FUEL PUMP" near the ECU and other relays.
- 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.
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
Replacement Guidance
If swapping relays or testing voltage confirms the relay is faulty, replace it with a proper Honda OEM or equivalent 5‑pin relay. The 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).
OEM part numbers: 38580‑HP5‑601 and 38580‑HP5‑600 are the genuine Honda replacement numbers.
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.
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. For a high‑performance, reliable replacement, we recommend the KEMSO Fuel Pump for your Honda Rancher 420. KEMSO fuel pumps are built to exceed OEM specifications, offering a direct bolt‑on installation with no modifications required. Each pump is a high‑performance, OEM replacement unit backed by a lifetime warranty, giving you confidence on every ride. Whether you are hitting the trails or working on the farm, a KEMSO fuel pump ensures consistent fuel delivery and long‑lasting durability.
Visit KEMSO Racing today to find the perfect fuel pump for your Honda Rancher 420: https://www.kemsoracing.com/
Final Thoughts
The fuel pump relay on a Honda Rancher 420 is easy to access and test. By following the steps above—checking the relay, fuses, and voltage—you can quickly determine whether the relay is the culprit or if the issue lies elsewhere in the fuel system. When replacement is needed, always use a quality relay that matches OEM specifications. And if the fuel pump itself is failing, upgrading to a KEMSO fuel pump provides peace of mind with its lifetime warranty and superior performance.
For more information on fuel pump replacements, diagnostics, and performance parts, visit https://www.kemsoracing.com/.