He may have wired in this controller, that your switch plugs into, as part of a voltage upgrade (and probably to get variable speed control too)-

Wingsmoto Aftermarket Controller 48v 1000w for Brushed Electric Motor Engine Scooter with Black Battery Connector Terminal https://www.amazon.com/dp/B07GBVXT4T/ref=cm_sw_r_cp_api_i_sO2TEb9Z8M5G5