3-way switch - In
a Les Paul or other guitars with two pickups, a three way switch selects
between the pickups. It also can select both pickups at the same
time. This is accomplished by the toggle portion pushing the contacts
to the appropriate pickup. (Note that the pickup selected is actually
on the opposite side of the switch than you would think; This is just a
quirk of the design.)
5-way switch - On Stratocasters
and other guitars with three pickups, this type of switch selects the individual
pickups as well as combinations of the middle pickup with the other two
(at least, that's the typical configuration; some guitars --mine, for instance--
sometimes have a few twists in their design). This is because the
"in-between" positions make contact with the pickups in the adjacent positions.
A 5-way switch also has the additional
feature of being built around two "poles," so it has two independent circuits
on either "side" (I say "side" in quotes because these switches come in
a confusing variety of configurations). These poles allow for additional
connections, including to the individual tone knobs as on a Stratocaster.
The lugs on each "side" of the switch are
numbered like this:
0 = "common" (all positions will
connect to here when selected)
To see how these are connected in a conventional
guitar, see the stock Stratocaster schematic.
Of course, if you're in doubt, you can always run a continuity test across
the lugs to figure out which connect to which in each position.
1 = bridge pickup
2 = middle pickup
3 = neck pickup
Note: There are other switches out
there that have more than two poles. These are usually clearly marked
as such (they also have more than 8 lugs to connect to), so it's kind of
obvious. These allow alternative connections that you can learn about
elsewhere on this site.