1986 Honda Fourtrax 350 Fuel Pump Wiring Diagram: Essential Guide for Diagnosis & Repair

The wiring diagram for the 1986 Honda Fourtrax 350 fuel pump is straightforward but critical for diagnosing power and ground issues. Here it is:

  • Fuel Pump Power Source: A red wire carries +12 volts from the main fuse block directly to the fuel pump when the ignition is ON and the engine is running. Power flows through a 10 Amp fuse.
  • Ground Connection: A black wire provides the ground connection from the fuel pump to the chassis or main grounding point. A good chassis ground is essential.
  • Circuit Operation: +12V flows from the fuse block, through the red wire to the pump. Electricity completes the circuit through the pump motor and exits via the black wire to the chassis ground. This completes the path needed for the pump to operate.

(The simplified wiring diagram explained below provides the specific path and key connections essential for troubleshooting.)

Understanding this basic wiring is fundamental to diagnosing why your fuel pump isn't working and getting your Fourtrax running again.


The heart of your 1986 Honda Fourtrax 350's fuel system is the pump. When it stops working, the engine stops. A surprisingly common cause of failure isn't the pump itself, but problems within its electrical circuit. Whether you suspect a faulty pump or need to trace down why it's not getting power, having the correct wiring diagram is the essential first step. This guide provides that diagram clearly and breaks down the entire circuit step-by-step for practical troubleshooting and repair.

Understanding the Fuel Pump's Role & Location

The 1986 Honda Fourtrax 350 uses a simple, yet reliable, low-pressure electric fuel pump. Its job is straightforward:

  1. Draw gasoline from the fuel tank.
  2. Deliver that fuel through the lines to the carburetor bowl.
  3. Maintain enough pressure to supply the carburetor consistently, especially under varying operating conditions.

Location: The fuel pump is mounted low on the chassis frame or engine cradle, typically under the seat near the rear of the fuel tank. Its position allows it to draw fuel upwards from the tank effectively. It's a small, box-shaped component with two fuel lines (inlet from tank, outlet to carb) and an electrical connector.

The Importance of the Correct Wiring Diagram

Honda's wiring harnesses are robust, but decades of heat, vibration, exposure to elements (mud, water, chemicals), and potential modifications can take their toll. Symptoms pointing to a potential fuel pump circuit problem include:

  • Engine cranks but will not start.
  • Engine starts but quickly dies (no sustained fuel supply).
  • Sputtering or lack of power at higher speeds under load.
  • Fuel pump makes no audible hum when the ignition is turned on (briefly) or while cranking.
  • Intermittent engine operation or stalling.

A generic wiring diagram won't help. The specific wire colors, connector types, and component locations changed over even slight model year differences. Using the correct diagram for your 1986 Fourtrax 350 ensures you check the right wires in the right places, saving time and preventing misdiagnosis that could lead to replacing a good pump or overlooking a simple connection problem.

Detailed Breakdown: 1986 Honda Fourtrax 350 Fuel Pump Wiring Diagram

Let's dissect the circuit completely. Imagine following the electrical current as it flows:

  1. Power Source (Fuse Box): All electrical circuits on the Fourtrax start with a power source protected by a fuse. For the fuel pump circuit:

    • +12 Volts originates from the battery.
    • This power flows to the Main Fuse Block (typically located near the battery).
    • Crucial Safety Component: A 10 Amp fuse specifically protects the fuel pump circuit and related components. This fuse is often labeled or color-coded on the fuse block cover.
  2. Power Delivery (Red Wire): When the ignition switch is turned ON and the engine is either being cranked or running:

    • Power is allowed to flow from the main fuse block.
    • The Main Power Wire: This +12V power travels primarily through a Red Wire to the fuel pump itself. The red wire connects directly to one terminal of the fuel pump's electrical connector.
  3. Ground Completion (Black Wire): For the pump motor to operate, electricity must complete a circuit back to the battery's negative terminal.

    • The Ground Path: A Black Wire connects from the other terminal of the fuel pump's electrical connector to a grounding point on the ATV's metal frame or engine block. This connection provides the essential pathway back to the battery's negative terminal. Warning: Frame rust, loose bolts, or paint can severely compromise this ground connection, preventing pump operation even if power is present.

Key Wiring Points Summary:

Element Color Function Failsafe Protection
Source Voltage N/A Battery power routed through ignition circuits Main Fuse (20A-30A)
Circuit Protection N/A Primary safety barrier for fuel system wiring 10A Fuse
Power Feed Wire Red Carries protected +12V directly to fuel pump None beyond fuse
Fuel Pump Component N/A Electromechanical unit pressurizing fuel None
Ground Return Wire Black Completes circuit back to battery negative terminal None
Termination Point N/A Chassis or engine ground (securely bolted bare metal surface) N/A

Fuel Pump Activation Control

Unlike modern vehicles with computer controls, the 1986 Fourtrax 350 fuel pump circuit is quite basic:

  • Manual Ignition Switch Control: When you turn the ignition key to the "ON" position, power flows through the fuse block to the pump. You should hear a faint hum for a second or two.
  • Run Position: Power remains supplied to the pump as long as the ignition switch is in the "ON" or "RUN" position.
  • Safety Cut-off: The circuit is not controlled by oil pressure or engine run sensors on this model. If power is present at the connector and the ground is good, the pump should run when the ignition is on. Important: The pump only runs when the ignition is ON or the engine is cranking/running. If it runs constantly with the key off, this indicates a serious wiring fault that needs immediate attention.

Critical Components Beyond the Wires

The wires connect the pump to power and ground, but other components are essential:

  • Fuse: As detailed, the 10 Amp fuse is the circuit's weak link intentionally designed to blow if excessive current flows (e.g., a short circuit). Always check this fuse first.
  • Electrical Connector: This simple plastic plug/socket (usually with two pins/cavities) connects the vehicle's harness to the pump. Corrosion inside these connectors or broken locking tabs leading to loose connections are frequent failure points.
  • Ground Point: This isn't a specific part you buy, but a location on the frame or engine block cleaned down to bare metal where the black wire terminates (often via a ring terminal bolted down). Rust, paint, or debris blocking metal-to-metal contact here prevents the circuit from working.

Common Failure Points Specific to the 1986 Fourtrax 350 Circuit

Knowing where problems commonly occur speeds diagnosis:

  1. Blown 10 Amp Fuse: The most common issue. Causes: Old fuse failing, a short circuit (bare red wire touching frame), a failing pump motor drawing too much current. Check it visually and electrically (with a multimeter) BEFORE anything else.
  2. Corroded/Bad Connections:
    • At the Fuse Block: Corrosion can build up on the fuse terminals or the contacts inside the block.
    • At the Pump Connector: Exposure to mud and moisture under the seat leads to green corrosion or bent pins. Unplug and inspect both sides of the connector thoroughly.
    • At Ground Point: The ring terminal end of the black wire bolted to the frame becomes loose or rusty. Scrape frame contact point and ring terminal clean. Tighten bolt securely.
  3. Damaged Wires: Look along the entire red and black wire paths. Common causes:
    • Fraying or breaking where wires exit the harness bundle.
    • Chafing against sharp frame edges.
    • Damage from rodents chewing insulation.
    • Brittle insulation cracking with age, potentially causing shorts or open circuits.
  4. Faulty Ignition Switch: While less common for only the fuel pump circuit (as other components would likely fail too), internal contacts in the ignition switch can wear out. Check for power at the fuse with the key ON to verify switch function before going after wiring.
  5. Failed Fuel Pump: Eventually, the pump motor itself burns out. Diagnose power and ground first to confirm the pump is actually dead.

Step-by-Step Troubleshooting Using the Wiring Diagram

Use this logical sequence with your multimeter:

  1. Confirm Symptoms: Engine cranks but won't start? No pump hum?
  2. Verify Fuel Supply: Is there fuel in the tank? Is the tank vent hose clear? Open the carb drain screw briefly to confirm absolutely no fuel delivery. (Have a container ready!).
  3. Visually Inspect Fuse: Locate the fuse block. Find the 10 Amp fuse. Remove it and inspect the thin metal strip inside - is it broken? Replace with an exact 10 Amp replacement fuse.
  4. Check Voltage at Fuse Socket (Key ON): Set multimeter to DC Volts (20V range). Touch the black probe to a good ground point (clean bolt on frame). Touch the red probe to each metal contact inside the fuse socket where you removed the fuse. You should read battery voltage (approx. 12.5V) in at least one side. If zero voltage, you have an issue BEFORE the fuse (ignition switch, main fuse, wiring). If you have voltage, proceed.
  5. Check Voltage at Fuel Pump Connector (Key ON): Locate the fuel pump. Unplug its electrical connector. Identify the cavity for the Red Wire (usually the cavity connected to the terminal connected to the red wire - match colors on both sides of the connector if possible). Set multimeter to DC Volts. Touch the black probe to a solid ground point. Carefully insert the red probe into the connector cavity matching the Red Wire from the harness side. With key ON, you should read battery voltage here. If yes, power is getting to the pump. If not, the fault is in the red wire between the fuse block and the connector or a bad connection at the fuse block.
  6. Check Ground Path Integrity (Harness Side Connector):
    • Reconnect the fuel pump connector temporarily for this test, or access the black wire pin/cavity on the harness side connector.
    • Set multimeter to Resistance (Ohms) or Diode/Continuity (symbol usually looks like )> or sound waves).
    • Touch the black probe to a clean bare metal point on the ATV frame (scrape paint off if needed).
    • Touch the red probe to the cavity/pin for the Black Wire on the harness side of the connector.
    • You should read a very low resistance (less than 1 Ohm) or hear a continuity beep. This confirms the ground wire from the harness connector back to the frame is good. If you get high resistance or no continuity, trace the black wire back, check connections, and clean the ground point thoroughly.
  7. Check Ground Path at Pump: If steps 5 and 6 are good but the pump doesn't run, disconnect the connector again. Set multimeter to Resistance/Continuity.
    • Touch the red probe to the terminal on the pump itself that connects to the Black Wire.
    • Touch the black probe to the fuel pump's metal mounting bracket or body. You should read low resistance/continuity. This confirms the pump's internal ground path is intact. A bad reading here means pump internal failure.
  8. Test Pump Directly (if Voltage/Ground Checks OK): Disconnect the harness connector. Get two jumper wires. Connect one jumper from the Red Wire pump terminal to the battery POSITIVE (+) terminal. Connect the other jumper from the Black Wire pump terminal to the battery NEGATIVE (-) terminal. Warning: Do this quickly. Sparks near gasoline are dangerous. Ensure pump outlet hose is disconnected and pointing safely into a container away from sparks/battery. The pump should run vigorously. If it doesn't, the pump motor is faulty. Replace the fuel pump. If it does run with direct power, the problem is in the wiring/connections/harness despite previous checks indicating voltage - re-examine connections and wires carefully.

Safety Precautions for Working on Fuel Systems

Gasoline is extremely flammable. Respect the hazard:

  • No Smoking or Open Flames: Work in a well-ventilated area away from sparks (including batteries!).
  • Disconnect Battery First: Always disconnect the NEGATIVE battery cable before touching fuel lines, pump wires, or electrical connectors to prevent sparks.
  • Relieve Fuel Pressure: Disconnecting the fuel pump connector while running or shortly after shutting off will relieve minor pressure. Cover connections with a rag when disconnecting fuel lines. Have a fire extinguisher rated for gasoline fires (Class B) nearby.
  • Prevent Spills: Have containers ready to catch fuel from open lines. Dispose of fuel and rags properly.
  • Handle Electrical Safely: Avoid shorting wires together. Ensure battery connections are clean and tight after reconnecting.

Finding Replacement Parts

Once diagnosed:

  • Fuses: Standard automotive blade fuses (10 Amp). Available at auto parts stores, hardware stores, online.
  • Wiring Repair: High-quality automotive primary wire (14-16 gauge). Soldering, heat shrink tubing, and automotive-grade electrical connectors are best for repairs. Avoid cheap crimp connectors.
  • Fuel Pump Connector: Look for OEM-style replacement connectors (often available as pigtails) through Honda dealers, ATV parts specialists online, or reputable harness repair shops. Match wire colors and terminal types.
  • Fuel Pump: Use the Honda OEM part number (e.g., 16710-HA5-671) for best reliability, or a well-reviewed aftermarket brand specifically listing compatibility with the '86 Fourtrax 350. Verify new pump matches inlet/outlet size and mounting.

Why Understanding This Wiring Matters

Relying solely on a shop manual picture isn't enough. Knowing the purpose of the red and black wires, the location of the 10 Amp fuse, and the grounding path allows you to:

  • Fix simple problems quickly (blown fuse, loose connection).
  • Avoid replacing a good fuel pump unnecessarily.
  • Perform repairs safely and correctly with confidence.
  • Save significant money on expensive shop diagnostics or incorrect parts.

Conclusion

The wiring diagram for the 1986 Honda Fourtrax 350 fuel pump reveals a simple circuit: protected power via a red wire and a ground return via a black wire. This simplicity is its strength, making diagnosis manageable for any DIY enthusiast. Armed with this diagram, the detailed component breakdown, common failure points, and step-by-step troubleshooting guide, you have the knowledge to effectively diagnose and repair the vast majority of fuel pump electrical issues on your classic Fourtrax. Remember safety first, start by checking the fuse and connections, and use a multimeter to confirm power and ground integrity before condemning the pump itself. With these tools, you can confidently keep your 1986 Fourtrax 350 reliably fueled and running strong.