Nah, I didn't drink before I was 21 either... for the most part. I know what you mean though, all my friends were always at parties back then getting intoxicated. Thats a good choice to stay away... although I'm basically an alcoholic now... maybe you shouldn't really listen to anything I say too much, I'm not exactly an outstanding role model for anyone...
Anyway, I'm not an electrical engineer by any means, but I'll give you what little I know on the subject. Someone with some actually intelligence jump in here if need be... watch for erroneous information. There are different wires between the high beams and low beams... they are actually 2 different bulbs. As far as one breaker for 3 relays goes, Im 99% sure you cant do that. The point of a relay is not only to take an electrical load off of a switch, but to cut out the problem arc when you flip the switch. A standard switch, when you flip it, goes from open circut to closed, I should hope thats general knowledge. The problem is there is a split second when opening or closing the circut where you have a gap small enough for the current to arc. When the current arcs, the circut can overload and blow a fuse, trip a breaker, or if none of the two are installed, fry the next weakest link. Things like a phone charger, a CB, or smaller lights and stuff like that, it doesnt matter as much. Those circuts dont take as much juice, so the gap in which the arc will jump becomes so minimal that it doesnt hurt anything. On headlights, they take some juice. When you pull the switch, theres enough current draw to create a little bigger arc over a bigger gap. This burns up your contacts on the switch eventually. What a relay does is re route the juice that the lights take so that it never goes through the switch. A relay generally has some kind of magnetic contacts that jump between open and closed so fast that theres almost no arc. With a relay, all that pulling out the headlight switch does is power up the relay. When power reaches the relay, it activates and takes power straight from the battery to the headlights. There ends up being one isolated circut between the switch and the relay, and another between the higher draw side of the relay and the headlights. Moral of the story? The side marker lights, cab lights, and things like that are smaller bulbs with less juice... they probably will be ok right off the switch if thats the way you wanna wire it. This is also why you cant have one breaker for 3 relays. If you put it anywhere on the circut with the switch, it would be pointless because thats the low draw circut. If you put it on the power source on the high draw side of the relays, or on the negative before ground but after the lights, you would end up breaking the circut every time you had all 3 things turned on. You could get a higher amp breaker so it could run all 3, but then you defeat the purpose of it any time you only use one relay circut. With one circut, even if theres a short, the breaker will be too high to open up from just one circut and you'll blow up a headlight bulb or a relay or God knows what else before the circut breaker even opens.
Circut breakers aint cheap, so I can see why you'd only want to use one, but keep in mind they dont blow like fuses. If you short something with fuses, you go buy new ones every time. When you short something on a breaker, you reset the breaker, its not junk.
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