| The value of the pot rarely matters actually, since they are usually just wired as a simple voltage divider. But, it does vary depending on the manufacturer, so try and work out what exactly is required before you start.
For a simple voltage divider, here's what I would do:
Open it up, gut it, except for the pot and the stereo jack socket (should be the input socket.)
The pot should have three terminals - pick one of the outside terminals and appoint it as "ground."
The opposite outside terminal is therefore now the "input" (if you will) and the middle terminal is the "output".
Usually, exp pedals use a stereo jack connector, or TRS jack (tip, ring, sleeve). Again, usually, the tip is the input (treadle-controlled voltage) to the device being controlled, the ring is the output from the device being controlled (a constant voltage) and the sleeve is ground. Wire up the stereo jack you left in the wah housing - connect using a TRS to TRS jack cable and Bob's my uncle.
You might find that the treadle works backwards at this point. If so, swap the two outside wires on the pot.
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niftydog
"My feet itch." Mike Patton | 
