2000 Yamaha YFM400FWA(M) Factory Service workshop Manual, Page 347Get this manual
SIGNAL SYSTEM 3.If the reverse indicator 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 socketNO CONTINUITY
2.Reverse switch Refer to "SWITCH INSPECTION"CONTINUITY
Replace the reverse switch
3.Reverse relay