On the 78 and I am sure other models as well, your ground is the largest wire of the three in the headlight subharness. Two smaller wires carry dc to the headlights and the larger wire carries it back. Bright/dim all depends on which circuit you ground at the combination switch.
What actual problem are you having? If its dim lights it is usually a ground somewhere. Not necessarily at the headlights. Remember, all of the electrical system is a circle and every problem can have an effect on another part of the system.
Problem is - both headlights dim while on normal, when flipped to birghts, the left headlight comes on full blast and the right one goes out completely. I have pulled and cleaned both column switches. I am almost sure it is a ground on the body. HELP!!
YES! check your fuses and the crimped connectors at the back of the fuse box. Resistance builds up and can cause all sorts of gremlins. The big, black spade connected wire in the steering column--disconnect it and you loose a lot of things including lights. H4 halogen lights? connecting the three wires at the back of the headlights in the wrong manner will cause that crap too! Usually when you solder the fusebox and clean the black wire with new fuses the problem will go away.
If you don't want it to come back, clean ALL the wire connections you can get to with contact cleaner and mechanical means, make sure all crimp connectors are tight (squeeze the female parts with a plires if need be), solder all the crimped connections you can get to (including the back of the fusebox)and when reassembling use a good silicone dielectric grease LIBERALLY on ALL the connections (I even lightly coat the fuse terminals and fuse ends). It will go away FOREVER (or until your switch fails...I'm working on that!)