Manual Headlamp Levelling, Detailed Description

Manual Headlamp Levelling, Detailed Description

On cars with manual headlamp levelling, the knob has 3 positions to the left of the headlamp position. These positions are used to regulate beam length. They are resistive multiplexing, which leads to an additional number of resistors in this variant. 5 resistors are internally coupled between +15 and ground. The switch knob straight up in the headlamp position gives normal beam length. High voltage is taken out in this position between the 4th and 5th resistor calculated from ground. Each step the beam length is to be moved closer to the car, voltage is taken out closer to ground, thereby sinking. Voltage is supplied from switch (684) pin 5 to pin 8 of the headlamps (663FL/FR). The headlamps also contain an electronic unit that governs the headlamp levelling motor in proportion to the incoming voltage level.