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How to cure electrical faults on your motorbike

Haynes electrical diagram motorbike motorcycle

Electrical faults on any vehicle are annoying, but on bikes, where you can be left stranded by the side of the road in bad weather, they can be your worst nightmare.

Electrical problems often stem from simple causes, such as loose or corroded connections. Study the appropriate wiring diagram in your Haynes Manual to get a complete picture of what makes up that individual circuit.  

Faults can often be tracked down by noting if other components related to that circuit are operating properly or not. If several components or circuits fail at one time, it may be that the fault lies in the earth (ground) connection, as several circuits are routed through the same earth connection.

Find an electrical fault on your bike with this video

Electrical fault checks on bikes

Continuity checks can be made with a continuity tester or a multimeter. Cheap to buy, these testers are self-powered by a battery, therefore the checks are made with the ignition OFF. As a safety precaution, disconnect the battery negative (-) lead before making continuity checks, particularly if the ignition switch is being checked.

If using a multimeter, select the appropriate ohms scale and check that the meter reads infinity ( ∞ ). Touch the meter probes together and check that the meter reads zero; where necessary adjust the meter so that it reads zero. Make the test across the terminals described.

A voltage check can determine whether current is reaching a component. Tests can be made with a multimeter set to the dc volts scale or a test light. Check that the multimeter leads are inserted in the correct terminals on the meter, red to positive (+) and black to negative (-). Incorrect connections could damage the meter.

The meter (set the dc volts scale) should always be connected in parallel (across the load). Connecting it in series will not harm the meter, but the result will not be meaningful. Voltage checks are made with the ignition ON. Connect the meter’s red lead to the power supply wire and the negative lead to a good earth or directly to the battery’s negative terminal.

Voltage checks are made with the ignition ON. Connect the meter’s red lead to the power supply wire and the negative lead to a good earth or directly to the battery’s negative terminal.

Earth (ground) checks are based on the fact that connections are made either directly to the engine or by a separate wire into the earth circuit of the wire harness. To check the earth on a component, use an insulated jumper wire to temporarily bypass its earth connection. Connect one end of the jumper wire between the earth terminal or metal body of the component and the other end to the motorcycle’s engine or frame, or if possible directly to the earth (-) terminal on the battery. 

If the circuit works with the jumper wire installed, the original earth circuit is faulty. Check the wiring for open-circuits or poor connections.