just because the headlight dimmer switch is new, doesn't automatically rule it good. most now, are offshore produced.
still sounds like the headlight switch is the main problem.
member crackedback [if my old mind remembered correctly. if not, please accept my apologies ! ] makes a GREAT relay kit for the headlights ! easy to install with his instructions, and reasonably priced as well. i used his kit on my buddie's 72 duster, and it worked GREAT !
for the money, you can't buy the material used in the kit and build one yourself unless you use CHEAP material and components, which his are all High Quality.
wiring can be problematic, but if you take your time, draw diagrams to help you keep track of the wires and the positions they go in, and use quality replacement parts, you can do a successful repair !