When both relays are open and the park switch is closed, the excitation to the motor is reversed. This causes the area swept by
the wiper to shift downward.
Thanks, SpannerTurner
This is the part I don't have in my manuals.
However, how can simply reversing a motor cause a mechanical gearbox/converter (which produces oscillating motion) to change its area of sweep? For example, if you change the direction of pedalling on your bicycle, it doesn't cause the pedals to go any higher or lower (top and bottom)
There must be something pretty magical about this gearbox
Cheers
NSEU
P.S. I'll leave the gearbox dismantling to the experts, I think