Headlamp Levelling Operation

Headlamp Levelling Operation
At each of the four headlamp levelling switch positions, the contacts in the switch connect through resistors with differing values, which in turn provide four differing output voltages.

The output from the headlamp levelling switch is on a UY wire to header C0293 LHD/C0289 RHD. The output is connected from header C0293 LHD/C0289 RHD on UY wires to both headlamp levelling motors. The headlamp levelling switch is connected on a B wire, via header C0760, to earth header C0018.

The difference in the voltage output from the headlamp levelling switch and the battery voltage is compared by a potentiometer in the LH/RH headlamp levelling motors. When the headlamp levelling switch is moved, the differing voltage causes the motor to operate until the potentiometer output equals the switch output. The motors stop and set the headlamps to a position which corresponds to the headlamp levelling switch position.

The input voltage to the headlamp levelling switch passes through the following resistors depending on switch position as follows:
Position 0 = 120 Ohm (R5) and 390 Ohm (R6)
Position 1 = 120 Ohm (R5), 20 Ohm (R4) and 390 Ohm (R6)
Position 2 = 120 Ohm (R5), 20 Ohm (R4), 100 Ohm (R3) and 390 Ohm (R6)
Position 3 = 120 Ohm (R5), 20 Ohm (R4), 100 Ohm (R3), 75 Ohm (R2) and 390 Ohm (R6).