headlight relays

Go read this page and here, too. I use 30A relays, one for both low beams and one for both high beams. Make sure you use first-quality name-brand relays (Bosch, Tyco, Omron, P&B), not no-name Chinese garbage. And run good, fat wire—14-gauge minimum, preferably 12ga) for all three wires to each headlamp: low beam feed, high beam feed, and ground. Run your grounds all the way to a good, proper ground, too; battery negative or alternator housing. Sheetmetal grounds aren't good enough.