Test the engine stop switch

Home mechanic (basic tools) · Time: 20 to 30 min (estimate)

The engine stop switch (kill switch) on the right handlebar lets you stop the engine without letting go. On many bikes, including the K-Light 125, it is also part of the starter circuit, so in the STOP position neither the ignition nor the starter works. A dirty, wet or broken switch gives no start, no spark, or cutting out over bumps. The key switch works in a similar way and is tested here too.

Safety

• Key OFF and battery negative disconnected before you open the switch housing or unplug its connector.
• If the switch does not stop the engine, you must use the key to stop it. Repair it before riding.

You need

• A multimeter on continuity.
• The wire colours. K-Light 125: engine stop switch green and dark green (PDF page 105); key switch red/white 1 to red, and red/white to orange/blue (PDF page 102).

Steps

1. Flick the switch between STOP and RUN several times. Sometimes this clears dirt from the contacts. Then try starting.
2. Follow the right switch wiring to its connector, often inside the headlight shell or under the tank. Unplug it.
3. Engine stop switch. Measure across its two wires. K-Light 125: in RUN, green to dark green has continuity; in STOP, no continuity. Wiggle the switch and the wires while watching the meter. A reading that flickers means a bad contact or a broken wire.
4. Key switch. Unplug the key switch connector. K-Light 125: in ON, red/white 1 to red has continuity and red/white to orange/blue has continuity; in OFF or LOCK, no continuity. Turn and wiggle the key while watching.
5. If the switch fails, open the housing (two screws on most bikes), clean the contacts with contact cleaner, and check for corrosion or a broken spring. See Clean a handlebar switch. If it still fails, replace the switch assembly.
6. Check the connector pins for water and green corrosion. Clean and seal: Clean and seal electrical connectors.
7. Reconnect everything and test: in RUN the engine starts and runs; in STOP it stops at once.

Check your work

• The engine stops immediately when the switch goes to STOP.
• The engine starts and keeps running in RUN, even when you wiggle the handlebar and the switch wires.

If it did not fix the problem

• Switch and key test good but there is still no spark: Test the ignition coil and plug cap.
• Key switch faults: Test the ignition switch.

Reference values (K-Light 125)