Scoot F.A.Q.Q. Why do my headlights keep blowing out?
One of the most common reasons headlights, as well as tail lights and running lights, repeatedly fail is from an improperly functioning regulator (sometimes referred to as regulator/rectifier or rectifier) that doesn't control voltage as it should. When voltage gets too high bulbs fail. One telltale sign of a bad regulator is when the light gets brighter and brighter until it ultimately fails. You may also find that when a regulator fails, multiple lights in the circuit blow out.
You can use a multimeter to find out if your lights are blowing out because of overvoltage.
- Disconnect the light from it's wiring connector/socket.
- Set your multimeter to measure volts (V). If the light is powered by AC (will only come on with the engine running, stator powered), set the meter to measure AC volts (VAC). If the light is DC powered (can be turned on without the engine running, battery powered), set your meter to measure DC volts (VDC).
- Put the black probe from your multimeter on the ground supply in the light's connector on the harness. This is often a green or black wire, but refer to a wiring diagram if necessary.
- Put the red probe from you meter on a power supply in the light's connector on the harness. Some bulbs will have two power connections. These may be for high and low beam if it's a headlight. In that case it doesn't matter which you connect to as long as the high/low beam switch is set to send power to it. If you're checking a tail light you may have one wire for the brake light and one for the tail light. Connect to the wire for the tail light. You may need to refer to a wiring diagram, or simply try the other wire if you don't get a reading. A tail light wire should have power all of the time when the scooter is running and the lights are on. A brake light wire would only show power when the brake levers are used.
- Make sure the scooter is secure and on it's center stand or otherwise supported so the rear wheel is off of the ground and then start the engine and turn the headlight switch on.
- Watch the reading on the multimeter as your rev the engine. You don't need to rev the engine as high as it will go, but at least get it to around 6,000RPM. Again it's very important that the scooter is secure. You don't want the wheel to touch the ground while the engine is revved up or it will take off. Be careful.
- When working properly, most regulators won't allow voltage to exceed about 15V. If you see much beyond 15V your lights are probably blowing as a result of the elevated voltage.
Touching the glass portion of bulbs with bare hands can also lead to premature failure. Wear gloves or be careful to only handle the bulb by it's base.
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