Hi Ian,
It's probably just that the arms are fitted incorrectly. When they stop at the bottom, are they in the right place? Most likely they will sit too high / not be at the bottom of the window.
You can remove the arm(s), theyre likely held in place by a bolt, and reposition them as theyre on a splined shaft.
Reverse light - if its not the bulb and there are no corresponding fuses blown, its most likely either the reverse switch on the gearbox or the wires to the switch are disconnected.
Hth.
Chris.