should always start with the basics first - - make certain the battery is holding a full charge - don't ASSUME it is good. Verify if the the battery connector halves (and charger connector) are cracked & making full contact or are pitted (can cause high amp draw & low voltage delivery) and battery cables are in good shape - R & R as necessary, then do the foot switch wire harness thing..

check your footswitch and wiring running to it