While it looks unusual, and is unique to the Moke, it is actually a simple DPTT (double pole triple throw) switch. The double poles are used for power and earth, and the triple throw is Off, Slow and Fast.
Here is a layout of the internal wiring -
And here is a photo of the back of the switch, showing the terminals -
The park mechanism works differently to most modern wipers which have a circular plate with cutouts and contacts that press against the plate. Moke wiper motors have a cam on the output gear which operates a small plunger, that in turn works a set of points behind the terminals. When on, the motor works continually. When swiched off, power is applied to the park wire which continues to operate the motor on low speed until the cam operates the points. Power is then cut to the motor and simultaneously the low speed brush is earthed through the brake wire (31b). The motor now tries to act as a generator, and stops almost instantly. Without this wire and braking effect, the inertia of the motor and arms may cause the points to close again, and the motor will complete another rotation, or the wiper arms may "bounce" off the bottom of the screen. Without power to the park wire, the motor will stop wherever you turn the switch off.
The internal wiring of the motor -
And the terminals on the motor -
The points -
Brush wiring and plunger (Brown-slow, Black-fast) -
The reduction gears, cam and plunger (Note the way the grease was applied) -
Making It All Work
Fortunately the wiper switch and motor have the same terminal numbering, with the exception of the power in wire (31 - Green) which is not needed on the motor. So it is just a matter of connecting the corresponding numbers.
The layout of the terminals on the back of the switch, as viewed from the rear -
And the layout of the terminals on the end of the motor -
The colour of the wires does not matter, apart from earth, which is always black, and green which is always fused power. But here are the colours according to the Leyland Black Book appendix:
30 - Green (Power from fuse to switch)
31 - Black (Earth)
53 - Red/Lt. Green (Slow speed)
53a - Blue/Lt. Green (Park)
53b - Black/Dk. Green (Fast speed)
31b - Black/Red (Motor Brake)
The slow speed wire (Red/Lt. Green) on my ' 79 moke changes to a pink wire in the harness, then back to it's original colours before it connects to the motor. As far as I can tell, this is not a resistance wire, but may have been on some models. All other wires (with the exception of the power wire, 30 - Green) connect directly from switch to motor.
If you are using a non-original switch, be aware the brake wire should only be earthed when the switch is turned off, and will pulse current as the points open and close when the wipers are working. Therefore, it cannot be connected directly to earth and must be wired through the switch.
On the other hand, the park wire could be connected to a constant power source, and seems to cause no problems.