Explaining High Beam Circuit?

[RustyPile]

Originally Posted by Richard

Lights are plug and play. Switching needed is done by the ballast harness (hid) or led driver harness (led) Check voltage at the stock headlight connector. If you have 12v at two terminals or 12v on one and a few volts on another, probably the dimmer switch is most likely bad. Dapper has a relay harness available to take load off the headlight switch that is mostly plug and play that would fix problem of "seeping voltage" as it isolates the lights from the switch and provides direct power from battery. But best to locate problem (dimmer?) It could be the old headlight switch causing a voltage drop as well. A DVM is your friend.

Not debating or disagreeing, but simply seeking information. If the lights are plug and play, why is all that other paraphernalia need to make it work?? Enlighten me, I'm intrigued by any headlight system that costs $300..