The 400f2 1977 had a switch change. The start switch had 12 volts +
from the key switch [ black wire ] It would power the headlight in
the released position. It would power the start relay in the pressed
start position. If your switch and the bike are different years, you
will have to change the grounding on the switch or the relay. If you
need a wiring diagram. Get in touch with me.
Good Luck, Rob