Relay

A relay is a switch operated by an electromagnet. A small current from a handlebar switch or the ECU energises the coil, which pulls a contact closed and lets a much larger current flow to a load such as the headlight, fuel pump, horn or cooling fan. This keeps heavy currents away from the switches and thin wiring.

Motorcycles usually have several relays, often grouped near the fuse box, plus a starter relay or solenoid that handles the very high current to the starter motor. Turn signal flashers are also a type of relay.

Symptoms of a failing relay are a click with no action, intermittent operation or a part that does not work at all. Relays are cheap and plug-in, so swapping in a known good one is a quick test.