Horn types
AC and DC: Most mopeds do not have a battery, so the electricity is all AC alternating current from the generator (magneto). Motorcycles and some mopeds do have a battery. Their electricity is DC direct current. Horns are made for either AC or DC. DC horns sound like a beeeeeeeep. The pitch is steady because the battery voltage is steady. AC horns sound like a wrong answer buzzer. The pitch goes up and down with the rpm of the engine. AC and DC horns look similar, but do not interchange. All modern scooters and motorcycles have 12 volt DC horns. They are common. Some older Taiwanese mopeds have 6 volt DC horns. AC buzzers are “old school” and are not on anything modern.
Factors that affect AC horn loudness
Internal corrosion: Used moped horns that are on bikes loose loudness after many years. That is from corrosion on the aluminum sound plate and the zinc-plated steel surface it buzzes against. Horns that have been kept in a sealed wrapper do not loose loudness.
Headlight on or off: AC moped horns are loud with the headlight off, but quiet with the headlight on. That is because the horn and headlight share the same generator power, which is not well regulated, and limited in wattage. When the headlight is off the horn gets 10-15 volts, and when the light is on it gets 5-8 volts. The effect gets worse the more watts the headlight uses.
Generator power: AC horn loudness depends on the generator power. You never know if a horn that works on a Peugeot for example, would work on a Puch, until you try it. Or it might work good on Puch at low rpm, but not high. Maybe visa versa on Garelli.
Voltage regulation: Before the mid-1980’s there was a lot less generator power, typically 6 volt 25 watts. With the advent of solid-state AC voltage regulators, generator power was increased, typically 12 volt 50 watts. The regulated AC voltage eliminated the problem of the horn getting loosing loudness when the headlight was turned on.
Factors that affect DC horn loudness
Internal corrosion: Used moped horns that are on bikes loose loudness after many years. That is from corrosion on the aluminum sound plate and the zinc-plated steel surface it buzzes against. Horns that have been kept in a sealed wrapper do not loose loudness.
Battery power: Motorcycles that have electric start have large batteries with plenty of power available for the horn. But pedal or kick start mopeds with small batteries can have a weak horn caused by a weak battery.
Horn testing
You cannot easily tell whether a horn is good or bad. You cannot easily look inside because it is riveted together. You cannot perform a valid test of it unless you have the moped it is intended to go on, running, with working horn wires and button.
Horns for Sale
6 volt AC horn, 18 watt $28 freshly-made in Italy