The only issue would be if you were to say press your knee controller without realizing it while you were using the foot pedal. You could let up on the foot pedal, but the machine would still run. The solution would be to add a double pole double throw switch to select either controller. The two center terminals go to pins one and two on the three pin jack, where the knee controller is wired now, two terminals go to the foot controller and the last two go to the knee controller. Amazon has 120 volt 20 amp switches by Gardner Bender for less than three dollars.