Wiring harness & fuses

How it works

The wiring harness is all the wiring linking the battery, starter, ignition, fuel injection, lights and controls. It is protected by fuses, which blow in a short circuit to protect the circuit concerned, and runs through many connectors. Most electrical faults don't come from an expensive component but from a bad contact: a corroded connector, a loose terminal, a rusty earth, a wire chafed against the frame. Charging-circuit connectors, which carry a lot of current, can even overheat and melt. A blown fuse signals a fault: fitting a new one without finding the cause, or fitting a higher rating, is dangerous. Badly wired add-ons (USB socket, alarm, heated grips) are another common source of faults and battery drain. Diagnosis is done methodically with a multimeter, following the wiring diagram.

Maintenance tips

• ✓Find where the fuse box is and carry spare fuses of each rating.
• ✓Always replace a fuse with one of the same rating; if it blows again, look for the short.
• ✓Clean and protect exposed connectors (dielectric grease), especially after winter.
• ✓Check the earth points (frame, engine, battery): a corroded earth causes random faults.
• ✓Wire accessories through a relay or a circuit designed for them, never by tapping wires at random.