I am modding a pedal for a friend and for some reason, he doesnt want it true bypassed but he does want an LED installed. All that I've done were with 3PDT switches. But i was thinking that if i use the 9v Battery and somehow tie it in with the witch i could pull it off. I'm not sure if he uses the battery or a 9v power supply for the pedal. But could i install the on/off LED for his pedal with simply a battery and a SPST switch?

tl;dr: can you install an LED on wah with simply a SPST switch?