There is a fully-automatic wiper system available, the Hella
raintronic, standard on some German cars. It's a relay which replaces
the stock one on the fuseboard, and a light-sensor to be stuck to the
windshield. It senses light-level drops and automatically turns the
wipers on with infinitely-variable sweeps from 1-60.minute.

Not cheap, but you don't normally have to bother turning it on or
off. I have one, but haven't fitted it yet.
--
Andrew Grebneff
Dunedin, New Zealand
64 (3) 473-8863
<andrew.grebneff@stonebow.otago.ac.nz>
Fossil preparator
Seashell, Macintosh & VW/Toyota van nut