To rewire a weed wacker, first disconnect all power by unplugging it, removing the battery, or pulling the spark plug boot. Open the housing to access the wiring, identify the faulty wire or switch, replace or reconnect it using proper connectors, and test the unit before fully reassembling. This process can often fix common issues like a non-responsive trigger or intermittent power without a costly repair bill.
Safety First: Disconnect All Power
Before you touch any wiring on your string trimmer, you must ensure it cannot accidentally start. This is the most critical step to prevent electric shock or injury from a spinning cutting head. The method depends entirely on your trimmer’s power source.
- Corded Electric Trimmers: Unplug the power cord from the wall outlet. Do not rely on the switch being in the “off” position.
- Battery-Powered Trimmers: Remove the battery pack completely from the unit. Set it aside in a safe location away from your work area.
- Gas-Powered Trimmers: Pull the spark plug boot off the spark plug. This physically prevents the engine from firing. For added safety, you can also drain the fuel tank or ensure the fuel cap is secure to prevent spills.
Never attempt to open the housing or work on internal components while the trimmer is connected to a power source.
Know Your Trimmer: Corded, Battery, or Gas
Identifying your trimmer type is essential, as the internal layout and rewiring procedures differ. While all three types have a trigger switch and wiring harness, their power delivery systems are distinct.
- Corded Electric: Has a long power cord that plugs into an outlet. The wiring runs from the plug, through the handle, to the trigger switch and then to the motor.
- Battery-Powered: Features a removable battery pack that slots into the base or handle. Wiring connects the battery terminals to the switch and motor.
- Gas-Powered: Contains a small engine with a fuel tank and pull-start cord. The “wiring” is typically limited to the ignition system, connecting the spark plug, ignition coil, and a kill switch.
In most models, the primary wiring and the trigger switch are housed within the handle assembly.
Tools and Materials You’ll Need
Having the right tools on hand will make the job smoother and help you avoid damaging the trimmer’s plastic housing or electrical connections.
- Screwdriver Set: A mix of Phillips-head and flathead screwdrivers to remove housing screws.
- Pliers: Needle-nose pliers are useful for gripping small wires and connectors.
- Wire Strippers: For cleanly removing insulation from wire ends.
- Crimp Connectors or Soldering Iron: Crimp connectors (like butt splices) offer a quick, solderless repair. A soldering iron with solder provides a more permanent, vibration-resistant connection.
- Heat-Shrink Tubing or Electrical Tape: To insulate and protect repaired wire connections. Heat-shrink tubing is generally more durable.
- Multimeter (Optional but Recommended): An invaluable tool for testing continuity in switches and wires to pinpoint the exact fault.
Step-by-Step: Accessing the Wiring
Once power is disconnected, you can safely open the trimmer to access the internal components.
- Remove Screws: Carefully remove all screws holding the handle or housing halves together. Keep screws organized, perhaps in a small container, as they may be different lengths.
- Separate the Housing: Gently pry the two halves of the housing apart. Be mindful of plastic clips that may also hold it together; forcing it can break them.
- Document the Layout: Before disconnecting anything, take a clear photo of the existing wiring layout with your phone. This is your reference for reassembly. Note how wires are routed and which terminals they connect to on the switch.
- Identify Components: Once open, you will typically see the trigger switch, the wiring harness, and connections leading to the motor (in electric models) or the ignition system (in gas models).
Identifying Wires and Switch Terminals
Understanding the basic wiring helps you diagnose the problem and ensure correct reassembly.
Wire colors are not universally standardized across all trimmer brands. Do not assume a red wire is always positive or a black wire is always ground. Rely on the photo you took or a wiring diagram if one is printed inside the housing. Common connections include:
- Power Input: Wires coming from the power source (cord, battery terminals, or ignition coil).
- Switch Terminals: The trigger switch will have two or more metal terminals where wires attach, often via spade connectors.
- Output to Motor/Engine: Wires that carry current from the switch to the motor or ignition system.
A simple continuity test with a multimeter can confirm if a switch is working: set the meter to continuity mode (often a sound symbol), touch one probe to each switch terminal, and press the trigger. A beep indicates a closed circuit.
How to Replace a Faulty Trigger Switch
A broken trigger switch is a common reason a trimmer won’t start. Replacing it involves careful disconnection and reconnection.
- Disconnect Wires: Note which wire goes to which terminal on the old switch. Gently pull the spade connectors off the terminals using pliers if needed. If wires are soldered, you will need to desolder them.
- Remove the Switch: The switch may be held in place by screws or clips. Remove it from the housing.
- Install the New Switch: Secure the new, compatible switch in the same position. Ensure it is rated for the trimmer’s voltage and amperage (this information is often on the motor label or in the manual).
- Reconnect Wires: Attach each wire to the corresponding terminal on the new switch, exactly as they were on the old one. Double-check your photo reference.
How to Splice a Cut or Broken Wire
If a wire is severed or its insulation is damaged, you can repair it without replacing the entire harness.
- Strip the Ends: Use wire strippers to remove about 1/2 inch of insulation from each broken end, exposing clean copper strands.
- Join the Wires: Twist the exposed strands of the two ends together firmly.
- Secure the Connection:
- With a Crimp Connector: Slide a butt splice connector over the twisted wires and use a crimping tool to compress the metal sleeve, creating a strong mechanical and electrical bond.
- With Solder: Apply heat to the twisted wires with a soldering iron and feed solder into the joint until it flows and coats the wires. Let it cool completely.
- Insulate the Repair: Slide a piece of heat-shrink tubing over the connection and shrink it with a heat gun or lighter flame (carefully). Alternatively, wrap the repair tightly with electrical tape. A proper splice should be insulated and able to withstand vibration.
Testing Your Repair Before Reassembly
Before closing everything up, verify your work to avoid having to reopen the housing.
- Visual Inspection: Ensure all connections are secure, no bare wire is exposed, and no wires are pinched where the housing halves meet.
- Continuity Test: Use your multimeter to check for continuity across the repaired wire or new switch. This confirms the electrical path is complete.
- Cautious Power Test:
- Corded: Plug it in, keep your body clear of the cutting head, and briefly press the trigger.
- Battery: Insert the battery and test the trigger.
- Gas: Reattach the spark plug boot and attempt a pull start (with the cutting head clear).
If the trimmer activates as expected, you can proceed with reassembly. If not, disconnect power again and recheck your connections.
When to Repair vs. Replace Your Trimmer
While rewiring can fix many issues, it’s not always the most practical solution. Consider replacement or professional service if:
- The motor is burned out, seized, or making grinding noises.
- The housing is cracked or damaged to the point it cannot be safely reassembled.
- The cost of replacement parts (like a new switch and connectors) combined with your time approaches the price of a new trimmer.
- The problem involves the circuit board (on some advanced battery models) or internal engine components you are not comfortable servicing.
For complex issues like motor rewinding or carburetor problems on gas models, a qualified small-engine repair technician is often the best option.
Frequently Asked Questions
Can I use any wire to rewire my trimmer?
No. Use wire of a similar gauge (thickness) and insulation rating to handle the current and resist heat and vibration. Using undersized wire can create a fire hazard.
My trimmer runs but cuts out when I tilt it. Is this a wiring issue?
This is often a safety feature (low-oil sensor on 4-cycle engines) or a fuel delivery issue, not typically a wiring problem. Check your manual.
How do I know if my switch is bad?
A multimeter continuity test is the most reliable method. If the meter shows no continuity when the trigger is pressed (or shows continuity when it’s released, depending on switch type), the switch is likely faulty.
