Motorcycle headlight modulator laws

Written by joanna swanson
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Motorcycle headlight modulator laws
A motorcycle headlight modulator must conform to federal regulations. (front of a motorcycle showing chrome bumper and light image by David Smith from

A headlight modulator is used as a safety device for motorcycles. The modulator changes the headlight intensity in a rapid pattern, making the headlight flash or flicker. The flashing of the headlight helps other motorists see a motorcycle and helps to prevent other vehicles from turning into a motorcyclist's path.

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Modulator Operation

According to the Code of Federal Regulations, the modulator must be wired so that both high and low beams work if the modulator fails. The modulating system must not draw more than .45 volts when used on a six- or 12-volt system. Wiring for the modulator must not be connected on the ground side of the circuit but should be located on the power side of the filament.

Headlight Intensity

A modulator must cycle from high intensity to low intensity at 200 to 280 cycles per minute. For at least 50 per cent of the cycle, but not more than 70 per cent of the cycle, the headlight must be working at its full intensity. Each cycle may not use less than 17 per cent of the headlight's possible intensity at any time.

Markings and Instructions

Each motorcycle headlight modulator must have certain markings. The modulator or its packaging must be marked with the wattage, both maximum and minimum, that it is approved for use with. The instructions must include a diagram that shows where and how to mount the modulating system. Light bulbs that are designed for use with modulators must be marked "motorcycle." This marking must be permanent and the letters must be at least 3mm high.

Modulator Installation

The headlight and modulation system must be located on the front of the motorcycle. For single-light systems, the headlight must be installed on the centre of the motorcycle front. For systems with two lights, the lights may either be installed on the centre line of the motorcycle or be symmetrically installed on both sides of the centre. If the lights are installed on both sides of the centre, the inside edge of the lights may not be more than eight inches apart. This applies to a system where both lights display the high and low beam and a system where one light displays the high beam and the other displays the low beam.

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