I think it's the same way with 4 headlight systems. I just looked up a '59 car wiring diagram (has the 4 headlight system) and they're separate circuits from the dimmer switch, and I doubt that the dimmer switch is any different than the 2 headlight system. Per the GMPartswiki, the dimmer switch was the same from 55.2 thru 60 for Chev & GMC trucks.

Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.