I've done it on a few cars, just cover up the electrical parts, and without a doubt you MUST use a pressure washer (normal hose just chucks out too much water).
I typically spray on some bilt hamber 'Surfex-HD' - it's brilliant stuff, just agitate it with a brush and rinse it off.
Lastly, I always start the car as quickly as possible, and let it heat up to dry out any water. (keep a can of wd40 nearby just in case )
Failing any of that, check out detailingworld, plenty of great advice on there