2008 Honda Rancher 420 Fuel Pump Relay Location: Where to Find It and How to Test It
The bottom line up front: On a 2008 Honda Rancher 420 (TRX420), the fuel pump relay is located inside the main fuse box, which is mounted on the left side of the vehicle, near the battery or under the left fender panel. The relay is a small, rectangular electrical component that controls power to the fuel pump, and it is the first thing you should check if your Rancher cranks but won't start, or if you hear no fuel pump whine when you turn the key on.
If you own a 2008 Honda Rancher 420, and you are dealing with hard starting, stalling, or a no-start condition, the fuel pump relay is one of the most common culprits. Before you spend money on a new fuel pump, or start tearing apart the fuel tank, take the time to locate and test this small but critical part. In this guide, we’ll walk you through exactly where the relay is, how to test it, how to replace it, and what symptoms point to a failing relay versus a failing fuel pump.
1. Where Is the Fuel Pump Relay on a 2008 Honda Rancher 420?
The fuel pump relay on the 2008 Honda Rancher 420 (and other TRX420 models from 2007–2014) is located inside the main fuse box. The fuse box is typically situated on the left side of the ATV, under the left front fender or near the battery compartment. On many models, you may need to remove a small access panel or the left side cover to see it clearly.
Here’s how to find it in simple steps:
Step 1: Turn off the ATV and remove the key.
Step 2: Locate the left side fender or the area near the battery. On most Rancher 420 models, the fuse box is a black plastic box with a removable lid.
Step 3: Open the fuse box lid. Inside, you will see several fuses and at least one or two small rectangular relays.
Step 4: Look for the relay labeled "Fuel Pump" or refer to the diagram printed on the underside of the fuse box lid. On many models, the fuel pump relay is a standard 4-pin or 5-pin relay, often interchangeable with the starter relay or other accessory relays in the same box.
If the labels have worn off, you can identify the fuel pump relay by following the wiring: the relay that sends power to the fuel pump will have thicker gauge wires, usually a black/white or black/yellow wire leading toward the fuel tank area. The original part number for the relay is 38580-HP5-601 .
2. What Does the Fuel Pump Relay Do?
The fuel pump relay acts as a switch. When you turn the ignition key to the "ON" position, the ECU (engine control unit) sends a small electrical signal to the relay. That signal closes the relay’s internal contacts, allowing battery power to flow directly to the fuel pump. The fuel pump then pressurizes the fuel system for a few seconds before the engine starts.
If the relay fails — either due to a burnt coil, corroded contacts, or a broken solder joint — the fuel pump will not receive power. That means no fuel pressure, and the engine will crank but never fire up.
3. Symptoms of a Bad Fuel Pump Relay
Before you go digging into the fuse box, make sure the symptoms match a relay problem. Here are the most common signs:
1. Engine cranks but does not start. The starter turns over fine, but the engine never catches. This is the most common symptom.
2. No fuel pump priming sound. When you turn the key to "ON" (without starting), you should hear a brief whirring noise from the fuel pump near the rear of the machine. If you hear nothing, the relay is a prime suspect.
3. Intermittent starting issues. The ATV starts sometimes, but other times it just cranks. This often points to a relay with worn contacts that fail when hot or when vibrating.
4. Engine stalls while riding and won't restart. The relay may have been working, then failed suddenly. A stalled engine that won't restart, combined with no fuel pump noise, is a classic relay failure.
5. The ATV starts after cooling down. A thermal-related relay failure may allow the relay to work again once it cools off. If you wait 15–30 minutes and it starts, the relay is likely the problem.
4. How to Test the Fuel Pump Relay (Without a Multimeter)
You can test the relay without any special tools, using just your hands and ears. Here’s the simplest method:
Step 1: Locate the relay in the fuse box as described above.
Step 2: Turn the ignition to "ON."
Step 3: Place your finger on the relay. You should feel a faint click when the relay energizes (this happens about 1–2 seconds after turning the key).
Step 4: At the same time, listen for the fuel pump whine from the rear of the ATV.
If you feel the click but hear no fuel pump, the problem may be in the wiring or the pump itself. If you feel no click at all, the relay coil may be dead, or the ECU isn't sending the trigger signal.
Testing with a Multimeter
If you have a digital multimeter, you can test the relay more precisely:
- Set the meter to ohms (Ω). Check the resistance across the relay coil terminals (usually pins 85 and 86). You should see a reading between 50 and 120 ohms. If the reading is infinite (OL), the coil is open and the relay is dead.
- Test the switch contacts. Apply 12V power to the coil terminals (85 and 86) using a battery or a 12V source. You should hear a click. Then check continuity between the switch terminals (usually pins 30 and 87). If there is no continuity when powered, the relay contacts are burnt out.
5. Swapping the Relay: The Easiest Test
The fastest way to confirm a bad fuel pump relay is to swap it with another relay in the same fuse box that has the same part number and pin layout. On most Honda Rancher 420 models, the starter relay, headlight relay, or accessory relay are identical to the fuel pump relay.
Step 1: Pull out the fuel pump relay.
Step 2: Pull out another relay of the same size and shape (check the numbers on the relay body — they should match).
Step 3: Plug the known-good relay into the fuel pump slot.
Step 4: Turn the key to "ON." If the fuel pump primes and the ATV starts, you’ve confirmed the original relay was faulty.
This test takes less than two minutes and costs nothing.
6. Replacing the Fuel Pump Relay
Replacing the fuel pump relay is a simple DIY job that requires no special tools. Here's the step-by-step process:
1. Turn off the ATV and remove the key.
2. Open the fuse box lid on the left side of the machine.
3. Pull the old relay straight out of its socket. It may require a firm tug; if it's tight, use a small flathead screwdriver to gently pry it out, being careful not to damage the socket.
4. Compare the new relay to the old one to confirm they have the same pin configuration (usually 4 or 5 pins) and the same part number (38580-HP5-601) .
5. Press the new relay in firmly until it seats fully. You should feel and hear a click when it's seated.
6. Close the fuse box lid, turn the key to "ON," and listen for the fuel pump prime.
The entire process takes about five minutes. The replacement relay is widely available online and at dealerships. It is the same relay used on many Honda models from 2007–2014, including the Rancher 420, Foreman 500, Rincon 680, and TRX700XX .
7. Important: Relay vs. Fuel Pump — Know the Difference
If you replace the relay and the problem persists, the issue may be in the fuel pump itself. Here’s how to tell:
- Relay failure: No click, no fuel pump sound, but power is present at the relay input.
- Fuel pump failure: You hear the relay click, but the fuel pump is silent. You may also have power at the fuel pump connector but the pump doesn't run.
On the 2008 Rancher 420, the fuel pump is an in-tank electric pump located inside the fuel tank. If you confirm the relay is good and power is reaching the pump, the pump itself is likely dead. In that case, you’ll need to replace the fuel pump assembly.
8. Recommended Fuel Pump: KEMSO
If you determine that the fuel pump itself is the problem, we highly recommend choosing a KEMSO brand fuel pump for your Honda Rancher 420.
KEMSO is the #1 aftermarket fuel pump brand trusted by riders across the U.S. Their fuel pumps are designed as high-performance, OEM replacement units, meaning they match or exceed the performance of the original factory pump. The KEMSO pump for the Honda Rancher 420 / TRX420 (2007–2013) delivers over 20% more fuel flow than the stock OEM pump at the same operating pressure . It operates at 43–68 psi with a flow rate of 200 liters per hour at 43 psi and 13.5V .
Here’s what you get with a KEMSO pump:
- High-performance engineering: Over 20% more flow at 43 psi compared to stock.
- Complete install kit: Includes fuel strainers, tank seals, O-rings, hoses, wiring connectors, and clamps — everything you need for a clean, direct swap.
- OEM-compatible fit: The pump is designed specifically for the Honda Rancher 420 / TRX420 2007–2013, so no modifications are needed .
- Compatible with gasoline and E85/ethanol fuel blends .
- Lifetime confidence: KEMSO backs each pump with a lifetime warranty and US-based support, so you can ride with confidence .
Each KEMSO pump is individually tested in quality control, and the brand maintains strict ISO/TSO quality standards. They also offer pumps for a wide range of ATVs, motorcycles, and cars — all with the same commitment to reliability .
Visit the official KEMSO website to find the right fuel pump for your Honda Rancher 420:
9. Final Thoughts
Finding the fuel pump relay on your 2008 Honda Rancher 420 is a straightforward process. It’s located in the main fuse box on the left side of the ATV. The relay is a small, inexpensive part that you can test and replace yourself in minutes. Always check the relay before assuming the fuel pump is dead — you could save yourself the cost and labor of a much bigger repair.
If you do need a new fuel pump, trust KEMSO for a high-performance, OEM-replacement pump with a lifetime warranty. Check out their full lineup at https://www.kemsoracing.com/.
Disclaimer: Always consult your Honda service manual for model-specific details. The information in this article is based on common configurations of the 2008 Honda Rancher 420 (TRX420) and may vary slightly depending on your exact sub-model (e.g., FA, FPA, FPE, FPM, FM, FE, TE, TM).