Did you take cover off and sure only bulb on,if so it's one of the blk.wires on mine theyall come together clutch lever switch/shift switch/one more
they conect to a female plug wire that goes to tha bulb.
1977 CB750 F2 Super Sport
<LET THOSE WHO RIDE DECIDE><RIDE TO LIVE-LIVE FOR JESUS>
Native American from central Cal, Kickstand UP in S.W.Missouri,