The headlight current goes through one of the two contacts inside the START button.(R-handlebar) Over time the plastic around the contacts inside the switch MELTS and causes an OPEN circuit. FIX 1: CAREFULLY remove the switch from the housing (NO SOLDERING/UNSOLDERING WIRES), then pry the side-clips of the switch out & pull the switch apart. (Catch the Spring!) Clean the contacts (knife) and re-assemble.