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USA moped tail lights: 1970’s and 1980’s USA moped models generally have different tail lights than European models. That is because of the 1972 and 1976 US DOT motor vehicle safety requirements for motor-driven cycles and motorized bicycles. The rear light must shine to the rear and the sides, and illuminate the license plate. The rear of the bike must have red side and rear reflectors. Putting the reflectors with the tail light eliminates the need for adding them on elsewhere. Also the bulbs are bigger, 15 not 9mm, because of higher watts required for the running light, 5 watts instead of 3, and for the brake light 10 watts instead of nothing.
The most troublesome US DOT requirement was that the brake light operation cannot cause the head light to get dimmer. This meant that the brake light had to be powered by a separate source coil in the magneto-generator. There was no solid-state voltage regulation until the mid-1980’s. The AC voltage was crudely regulated by generator magnetism, rather than a external mechanical or electronic device.
Internal ignition ground family: Some US moped versions had an additional source coil to operate the brake light, such as Puch or Batavus (Bosch magnetos). On these the brake light wires never cause the engine to not run. The ignition source coil is grounded internally, inside the generator. So the ignition is never affected by any of the lights.
The brake light only needs to be matched with the generator source coil, usually 6 volt 10 watt. Unlike your house, a higher wattage bulb makes less light. If a 6V 18W bulb is used, it will be dim. If a 6V 5W bulb is used, it will be too bright and burn out.
External ignition ground family: Some US mopeds use the ignition source coil to operate the brake light, such as Garelli or Minarelli with (CEV magnetos). On these the brake light wires can cause the engine to loose spark and not run. If the connecters or wires are corroded or loose, on the brake light wires, the engine will stall when the brakes are applied. If the brake switch wires up at the handlebars are also loose, then the engine will not ever “have spark”. Removing the tail light assembly, or changing it, can cause these bikes to not run.
The brake light needs a 4 ohm (10 watt max) resistor in parallel with a 6 volt 10 watt bulb #81, or just a 6 volt 18 watt bulb #1129, or a 6V 21/5W #1154 dual filament bulb. For a brighter brake light but a weaker ignition spark, the resistor can be 6.8 ohm 10 watt.
Modern family: After the 1980’s, thankfully, there were no more mopeds with external ignition grounds. They had internal ignition grounds. So the brake light wires never cause the engine to loose spark. Their solid state AC voltage regulators allowed all the lights to run off of the same generator wire, yet still stay the same brightness as additional lights (brake) were turned off or on. The modern family also uses 12 volt bulbs instead of 6 volt.
The brake light bulb does not need to be any particular wattage. Just like in your house, a higher wattage bulb would produce more light. You want the brake light to be brighter than the tail light, for safety, but it doesn’t need to be.
Price List: Prices are for each item. Bright green means new. Dark green means used. N/A means not available.
Screws: M means metric machine screw M3, M4, M5, M6. ST means self tapping screw (for plastic).