The head light switch wire goes to the dimmer switch. Two wires then go from there to the headlight junction blocks, then to the high and low beams.

I think you are right on about what the H, S and R mean. It should be easy to determine with your multi-meter though.

"It's just a phase. He'll grow out of it." Mama, 1964

1956 Chevy 1/2-ton 3100
1953 Chevy 6100 "The Yard dog"
1954 GMC Suburban Now with a new proud owner.