Nowaday's, say in a parker, you might have a peizo and magnetic outs to go to dedicated amps. Way back when you might have each pickup to a separate out into separate amps, such as rickenbacker offered amoungst others.
You could use a stereo lead to supply power to a guitar, but more often it is used as a switch so that the internal battery is disconected when the battery is pulled out, just like in a stompbox.
There have also been some interesting "stereo" guitars. Van Halen had one which had pan pots for each string so they could be spread across two amps.
The guitarist in one of my favorite groups, The Merman, has three leads, (one for each of his Strat's pickups) going into three different effects and amp chains. The mix of these is controlled by volume pedals so that he can vary and mix very different sounds on the fly. Often he'll have a clean reverb laden sound, a highly effected sound and a fuzzed out sound and combine them in really interesting ways that works well in the trio novo-surf format where you want to make a lot of noise.
With a more conventional each pickup to a different amp and effect chain, each pickup could have it's own unique amp and effect sound that could be changed as easily as switching the selector.
Of course you got to have the amps to make it work, though it is possible with a multichanel amp...it's not as effective as having separte speakers to drive it. You can also get stereo amps, but these are generally geared towards stereo effects as stereo guitars are so rare these days.
If piezo equiped guitars continue to take off though, amps may follow through with combination high gain and clean channels...some of this is already happening with the large range of "acoustic" amps now being made!...pete
Mr D.I.Y. Sustainer ;-) [/IMG]New Project...'jazz strat' ... Seagull project and mini PA amplification
so if i put 2 amp outputs on my guitar i could have 1 amp output for each pickup then use a switch to make it both out of 1 amp jack so i have 1 am for each pickup or with a flick of a switch i can have both pickups through 1 amp