[408cobra]

You have two relays one for high beams and one for low beams you run a 1/2 watt diode between the turn on circuit for the high beam relay to the turn on side of the low beam relay. When the high beams are turmed on it supplies current to the relay for the low beams as well. When just the low beams are on the current only flows in one direction in a diode so the high beams remain off. Hope this helps it sound difficult but is actually pretty simple.