Replace a bulb

This job takes out a dead or blackened bulb and fits the correct new one. Do it when one lamp is dark and the others work, or when a headlight bulb glass has turned black or brown. Many modern bikes have sealed LED lamps with no bulb inside: if you cannot find a bulb holder, the whole lamp unit is the part, so stop here and go to Test a lighting circuit before you buy one.

Safety

• Turn the key off before you start. A bulb that has been on is hot enough to burn you; let it cool.
• Halogen headlight bulbs run under pressure and can break. Wear glasses when you push a stiff bulb into its holder.
• Support the bike on its centre stand or a paddock stand so it cannot fall while you work on the lamp.
• Do not fit a bulb with a higher wattage than the original. More watts means more heat, melted holders and burnt switch contacts.

You need

• The new bulb. Take the old one to the shop. Match the cap type (the metal base), the voltage (12 V on almost all modern bikes, 6 V on some old ones), and the wattage printed on the old bulb or in your manual.
• Twin-filament bulbs (tail and brake in one bulb, or high and low beam in one bulb) have offset pins or tabs. They fit only one way.
• K-Light 125 bulb types: headlight H4, front position light W3W, indicators R10W, tail and brake light P21/5W, number plate light W5W. The manual does not give the headlight wattage, so read it on the old bulb.

Steps

1. Turn the key off. Find the lamp with the dead bulb.
2. Remove the lens screws, or the headlight unit fixing (on the K-Light 125 the headlight unit comes off after removing its locknut). Keep small screws in a cup.
3. Look at the old bulb before you remove it. Note which way the pins or tabs sit.
4. Remove the bulb. Push-and-twist bulbs: press in, turn anticlockwise, pull out. Wedge bulbs: pull straight out. Headlight bulbs: unplug the connector, take off the rubber boot, unhook the spring clip.
5. Check the old bulb. A broken wire inside (filament), a black or brown glass, or a loose base confirms it was dead.
6. Check the holder. Green or white powder, burnt plastic or a loose contact means the holder needs cleaning or replacing; see Clean and seal electrical connectors.
7. Hold the new halogen bulb by its metal base only. Skin oil on the glass makes a hot spot and shortens its life. If you touch it, wipe it with a cloth wet with alcohol.
8. Fit the new bulb the same way round as the old one. Refit the clip, the rubber boot and the connector.
9. Turn the key on and test the lamp before you refit the lens. For a headlight, test low beam, high beam and the flash (pass) button. On some bikes the headlight comes on only once the engine runs.
10. Refit the lens. Check its rubber seal sits in its groove so water stays out. Do not over-tighten plastic lens screws: they strip.

Check your work

• The lamp lights at normal brightness and does not flicker when you tap the lens.
• Both filaments of a twin bulb work: tail light on, then brighter when you pull either brake.
• Indicators flash at their normal speed on both sides.
• After a headlight change, check the beam still points where it should: Aim the headlight.

If it did not fix the problem

• New bulb also dark: Test a lighting circuit.
• Bulbs keep blowing: go to Bulbs keep blowing.
• Indicators still flash fast after a bulb change: Indicators flash too fast.

Reference values (K-Light 125)