I have a 1993 yamaha moto4,I replaced key switch and it worked until i moved the forward/reverse lever,also no reverse light i also changed the neutral sensor,but nothing.
thanx in advance

 

Must be 15 years since I worked on one but, as a rule, bikes back then had separate switches in the engine cases for neutral and reverse, so changing neutral switch won't alter the reverse switch circuit. Yamaha normally have an incredibly complex neutral lock out circuit, preventing starting when not in neutral. Best to get the wiring diagram and check how it works.

Just a thought, but if you didn't fit a correct ignition switch, you may have blown the main fuse, that would stop warning lights and starter from working.