Please keep in mind you don't install relay protection for voltage. A high draw of amps is what you need relay protection for. Amps are the spinach that gives Popeye (the voltage) the strength to hit Bluto hard enough to send him off to Mars. If you don't have enough volts being delivered to your headlights, you have a problem somewhere...and that generally means you won't have enough amps either. As Bill said, the dimmer switch and the headlight switch are likely suspects. I posted a repair tutorial for the headlight switch. When those get messed up you don't get enough juice going through the contacts any longer and the dimmer switch gets wet, dirty, etc and that causes it to suffer. Here is the headlight tutorial:
http://tinyurl.com/2uy3ubr8
