I’m having some trouble with a second hand DOD envelope filter I bought recently. The pedal works fine when plugged in at first, the switch works to turn it on and off, but as soon as it is all connected to the bass and amp, the pedal turns itself on as soon as I play a note. If I hold the footswitch down while playing, then the effect will turn off, but as soon as I release my foot it turns itself on again. Any ideas as to what may be causing this?
Faulty footswitch or maybe crossed or loose wires inside at one of the jacks. Just this week I had to solder a wire to the jack of a pedal I'm trying to sell. I had bought it new, and it's seen little use, but it's about 30 years old (!) and the wire had disconnected from its solder joint. (Boss OS-2 if you're wondering.) Open her up and check the connections.
Could be the footswitch and/or the jacks are just dirty. Get some spray contact cleaner and scrub those out. The actual switch mechanism is a little square plastic doohickey hidden underneath the big switch plate that you step on.