Normally it just beeps if there is a trailer lamp connected & an indicator is powered (UK tow regulation). The original unit was modified to also beep as an added safety feature, when reversing (with or without a trailer).

HOW IT WORKS

The trailer lamps are powered via power diodes D2 & D4 (1N5401) & the voltage drop across these turns on either of the 2 small PNP transistor to power the small buzzer via a low power steering diode D3 or D5 diode (1N4001). The additional reversing beeper uses a flashing LED in series with buzzer & a diode to give the same effect, this time as public warning. The 10uF capacitor is needed to stop the buzzer AC pulses affecting the LED internal timer. The flashing LED is the smallest flasher unit of its size.

LOCATION

This circuit is located at the rear, behind one of the lights clusters as it needs to be connected to both indicators & a reversing light feed, & be audible both to the driver and nearby pedestrians.

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