Speed swith mode
1 = 3-positional switch; speeds 1, 2 and 3 are used.
2 = one button; pressing will cycle three speeds:
1 -> 2 -> 3 -> 1 -> 2 -> 3 ...
3 = ?
4 = one button; pressing will cycle four speeds:
1 -> 2 -> 3 -> 4 -> 1 -> 2 -> ...
If no button/switch installed - speed 2 is used.