You can use the original wire to the headlights from the relays. The wires from the dimmer switch control the two headlight relays, high beam turns one off and on, low beam turns the second one off and on. But you have full alternator voltage feeding the relays and then the headlights through the original wires. You aren't upping the amperage just supplying the headlights with full 14.7 volts. When stock, the headlight circuit starts at the main junction goes through the firewall junction blocks, to the headlight switch to the dimmer switch then to the headlights. Every junction and switch is a potential voltage drop. Mine was about 10 volts at the headlights, now it's 14.7 volts. The difference is surprising! I replaced the wires but it's not necessary, just cut the wires at the relays and have them control the relays and use the rest to power the lights.