The effect is turned off when the correct pin is grounded. The light turns on when the pin is open and the light is grounded.
The original foot switch had little backlit name labels for each effect. The bulbs were turned on slightly through the 300 ohm resistor so that you could read the label. When the effect was turned on the bulb lit up to full brightness.
If you want to use leds instead of the bulbs you just need to use a series resistor to limit the current through the led. You can also eliminate the 330 ohm resistors.
Been to the parts store twice now, and both times I forgot to pick up the 1N5359A Diode! DOH!
So, I'll have to wait until monday to see if it works.
Radio Shack doesn't have it.
As far as I've been able to find out, it's a Zeener Diode that's a 24V regulator. (?)