1984 Vt 500 Ascot. The headight does not always come on when the bike is started.

I had the same problem. Disassembled the starter switch few times and every time it was either starter or headlight working. So I left it to start the starter and just jumped other two contacts straight at the harness. Headlight always stays on even if you press the start button, but it doesnt look as a trouble to me.

Try cleaning your starter button. If it continues to malfunction you may have to replace the right switch assembly. Your starter button is a two position switch. It first turns off the headlight, then it activates the starter solenoid. When your fuses, battery, wiring. and wiring connections are good usually you are dealing with a bad button/switch.