84 yamaha 200 not starting with key in light position

[Lakcountry1]

Key in on position bike will start but if you turn it to the position to turn on the headlight the bike does nothing at all and if its running and you turn it to the light position it kills the bike. Where should I start first? Im pretty good with electrical but I don't have a diagram of this unit.

[350for350]

If I remember right, that's how it's supposed to work. The engine isn't supposed to run in the "headlight" position. The headlight should come on while the engine's running. In fact, on the Yamahas that I used to have, I never did use that "headlight" position on the key switch.

[ATC King]

http://www.oscarmayer.net/atc/manuals/

https://threewheelermanuals.com/yamaha

All of these trikes are so old, virtually nobody cares about the manuals being posted for free. If you come across a site that takes donations, throw a few bucks their way. It takes time to makes these available.