2001 Yamaha YFM660 Raptor Factory Service Manual, Page 311Get this manual
SIGNAL SYSTEM CHECKING THE SIGNAL SYSTEM 1.If the tailbrake light fails to come on: 1.Bulb and bulb socket
NO CONTINUITY
Check the bulb and bulb socket for continuityCONTINUITY Replace the bulb andor bulb socket
2.Brake switches Refer to "CHECKING THE SWITCH"CONTINUITY
NO CONTINUITY