several things can cause the problem try to start with simple things first, 1 tail light has to bee good and working, kill switch can be grounded out usually the grommed is bad and lets short out disconnect the black wire going to it if has spark then fix last is cdi unit i forget how to check but you can buy engine repair manual from r&d may co that tells how to check. their add is 152 west mill st. bloomfield in. phone is 812-384-3612. also i am looking for twist throttle and light and horn switch for a 78 amf roadmaster if you can help please contact me. george mikesell 644 republic rd jamestown ks, 66948 e-mail gmikesell@nckcn.com phone 785-243-0709. thank you