One way to approach using relays is this way, use the headlight switch,or any other switch, to turn on the relay. The load goes from the battery thru the relay to the lights. The oem way is battery, switch,to the light. For several years now,all car manufactures have gone to the relays method in their wiring. In many cases,depending on what circuit is being used, the switch on the dash is used to switch ground to activate the relay,not power. The advantage to both is to eliminate the amount of heavy draw wiring in behind the dash,esp in vehicles with a ton on wiring. In the case of my 54 3100, i used a relay for my back up lights.The trans switch switches ground and key turns on power to relay. This eliminates power having to go thru trans switch. I probably wouldn't do it this way for headlights, just light switch to activate relay. Not necessary but fun, if a person likes wiring ,the sky is the limit in what can be done.
