If I don't have a wiring diagram, and it worked before the switch replacement, I normally use a continuity tester on the old one, and then find the corresponding terminal connections on the new switch. Essentially, you just draw a contact diagram for the old one, and find the terminals on the new one that have the same contacts. It only takes a minute or two. I usually use a multimeter because that's what I'm used to using, but when necessary I use a torch battery and a globe. There are lots of options.
