Control function: The failure of a direction indicator in a motor vehicle or trailer has to be shown to the driver either acoustically or by means of warning indicator lamps. HELLA flasher units ensure such control by means of the following: 1. Doubling of the flashing frequency (e-controller) or 2. Control lamp switch-off system (p-control). LED direction indicators conforming to ISO 13207 can "communicate" with the flasher unit. The flasher unit checks a firmly defined energy requirement at a firmly defined time: Exactly 21 W at the time of 100 – 130 ms after each switching on of the direction indicator. The energy requirement or "pulse" corresponds to that of a bulb in this case, meaning that the flasher unit notices no difference between a bulb and an LED lamp that conforms to ISO 13207. The advantage: Bulbs and ISO LED lamps can be operated in any combination on a flasher unit that conforms to ISO 13207. This is relevant both for vehicles that are frequently operated with different trailers and also for manufacturers who wish to offer several variants of the lighting system without having to modify the underlying electronics.