We shall be driving from Germany, through Switzerland to Italy. We may spend a night in Switzerland. I have a Schengen Visa (South African Passport)
You don't require any additional visa, as Switzerland is a schengen country itself - while not a member of the EU, it is a part of Schengen (and several other EU-related agreements).
If you wish to drive on a motorway/autoroute however, you will need a pass/sticker affixed to your car, called a Vignette. This can apparently be bought either online or at a border crossing.
Switzerland is member of the Schengen area. So you don't need any extra visa to enter Switzerland.