Re: How do leslies work?
Most Leslies (especially the old wooden-cabinet, tube-amp ones) get their control and audio through a big multi-pin connector. The line-level signal preamp and the stop/slow/fast switching all come through the cable, and Hammond organs were fitted with option kits to provide the preamp and control switches.
When rock & rollers started using them with non-Hammond "combo" organs, the preamp and switches were still needed, but were not built into the organ. So, LEslie made the "combo preamp". Looks like this:
You plug the guitar into it to act as a preamp, and the footswitches control the rotors. There are different model preamps for different Leslies, with from 1 to 4 footswitches.
There are other DIY ways to run a guitar into a Leslie, if you get the right pinout for your speaker and hook up the right stuff.
This is for Leslies with amplifiers in them. In general, wooden-cabinet Leslies have tube amps, the black-tolex-and-aluminum-trim "Pro Line" Leslies are solid state.
Of course, some Leslies have no amp at all, just speaker(s) and rotor(s). This includes the Fender Vibratone and sisters Leslie Model 14 and 16 (IIRC). In those cases, you need some sort of speed-control footswitch, but use an external amp head to power the speakers.