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Wiring Question for '39 Special

Guest myfirstbuick

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Guest myfirstbuick


I'll throw this out for all the electrical gurus - I have an understanding of home electrics so this puzzles me on my car... I am doing a re-wire starting with the headlights. According to my shop manual diagram, it shows 16 gauge wire coming from the headlight switch and going to the headlights. It has a branch off wire that goes to the dimmer switch using a 12 gauge wire.

Why the different gauges? I don't understand and would like an explanation because it's my understanding that the 12 gauge wire is overkill branching off from a 16 gauge wire.


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Guest imported_JPIndusi

Good question and I will check some wiring diagrams I have for 48 Buck Special. A possible explanation is that each individual light might be fed by a 16 gauge line, but the single dimmer switch feeds both upper beams, essentially it carries current for two lights.


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  • 2 months later...
Guest DaveCorbin

All of you are on the right track sort of. The headlight switch on a 39 is complicated by the fact noted above of the city/country mode in relation to the Hi-Low beams. The dimmer switch has to carry the current for both lights, so it needs a 12 GA both ways. There are 2 wires to each headlight(4 total), one for HI and the other for Low. In city mode on the switch, the dimmer moves both lights to Hi or Low. In country mode, only the left headlight goes Hi-Low.

Just to really set your head spinning, the same setup is used on a RHD car, except everything runs exactly the other way, which means that the bulbs also have the relationship of the internal elements reversed. Use both hands with your index finger pointed out to illustrate these combinations for yourself and you'll see what I mean.

I rewired my 39 Roadmaster about 25 years ago and about went nuts tryingto figure this out!

Regards, Dace Corbin

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To clarify, if I may, the left headlight (driver's side) points toward the right side of the road, illuminating the shoulder. This is the one that stays in high beam mode on country setting. The right headlight (passenger side) is the one that would blind an on-coming driver. It's the one that switches from high to low with the foot switch.

On the '38, the fender lights come on when the foot switch toggles to low beam, they go off when toggling to high beam.

We may be saying the same thing.


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