could be a short somewhere if you dont have power to the switch, keep tracing it back to plugs at the battery and such. it could be a bad regulator as well. ive seen it on snowmobiles, not so much a 400 but anything is possible. especially if you dont find any ground out areas or blown fuses. check continuity across all wires in the set for the lights in the harness that connects across the front and back to each disconnection point.
good luck with it, let us know what the result was.
steve
2019 Maverick X3 XDS Turbo R
2003 TRX 400EX
2016 HONDA RANCHER