There 2 knobs that controlled via 2 custom datarefs, for left and right wipers respectively.
les/dc3/iceRain/mnp/wiper_switch_L
les/dc3/iceRain/mnp/wiper_switch_R
Also the landings lights are controlled via those datarefs:
les/dc3/elecSys/lighting/L_ldgLit
les/dc3/elecSys/lighting/R_ldgLit
May be, some time in the future, change the controls to be custom commands, but because many systems has been customized, might not be possible to use default commands.