Technical using original headlight switch for 12V, 39 Ford

Ok, I have a new Rebel Wiring harness for the Std Tudor. I want to use the original light switch in the column/horn button area. I'm not worried about bulbs, grounds, not even worried about wire length. My only concern is terminal availability within the switch. I see several and of course will need the OG diagram to sort it all out. So the question or discussion topic is whether or not there's any caveats to this attempt. I see the brass tabs and such throughout, yet knowing 6V is usually higher amperage my brain is telling me that my 12V regular bulbs will be ok. Anyone done this?

 

I would use the switch to turn on relays going to the lights. JMO

Sent from my XT1526 using The H.A.M.B. mobile app

 

Also be sure to start with original switch, rotor, and contact plate in the switch...cut the plate off of an original harness and solder up the relevant wires to it. Everything in there that is reproduced is reproduced badly! Most repro contact plates have push-on terminals, originals are soldered in. Service bulletins plus color coding on original wire stumps will allow you to figgeritallout. I believe '39's, and maybe '37-9, have floor dimmer switch so the switch at bottom of column is simpler than earlier Fords.
Switch shaft turning with steering wheel plagues people working with these...switch shaft must be straight and smooth, Woodruff key at steering wheel must be the Ford part and not a generic hardware store one.

 

As long as the switch is in good electrical and mechanical condition, there's no reason it shouldn't work. Checking resistance through the switch wouldn't hurt, and maybe dosing it with DeOxit contact cleaner would be cheap insurance. If switching to halogen lamps, I'd do the research to determine original wattage @ 6V vs new wattage @ 12 to make sure you don't exceed the switch current ratings. But a 12V lamp can have double the wattage at the same current, so as long as you don't go for high-wattage 'off road' lamps you should be fine.

 

Ohms check won't tell you much, unless it was so corroded that it was obviously scrap.

Measure the voltage drop while under load. Positive battery post to positive headlight terminal for example. High resistance will cause switches to run hot, that's why relays are popular.

 

Have my 37 original switch hooked up to 12 volts.
This switch is at the end of the column. This switch includes separate positions for park, high and low beams. Works great.
When wiring, I just fired it up with 12 volts and armed with a test light marked each terminal for identification. Took some work as some wires attached to more than one terminal. Used to have the layout but damn I can't find it.

 

I believe the multiple terminal wires would be tail light, hooked up to come on with any headlight/park position.
A very hasty check seems to indicate cars got a floor dimmer for '38-9, simplifying headlight wires to just a single lead out to dimmer.

 

I did a 35 ford coupe for a customer and he wanted the stock switch to work. I used the switch to run relays for the lights. That was about 5 years ago and it is still working fine.

 

Yes Bruce, a dimmer switch gig in this one. Part of the reason I'm inspired to do this. Well that and I think it's cool. I'm going to run just normal 12V bulbs. No halogen/LED/blah,blah "improvements". The reason for 12V at all is for a bitchin sound system. I still want the overall look nice and vintage and the function to be as normal Ford as can be. I have all of the switch, even have a spare mast that's also straight as a pin. I did notice the soldered wire ends, a little put off by that as my Packard stuff is screw on terminals. Easy to correct if a "senior moment" screws up the layout

 

Basically with any switch you just want to be sure that the switch will handle the load your putting on it. A 6v switch in good working order should be fine as they are built heavier than the 12v. If your switch won't handle the load then you would want to relay it, turning the wires into trigger wires for the relay and taking the load off the switch. Looks like a lot of good advice from everyone!

 

You might want to relay it either way. There's usually a fair bit of voltage loss through switches, causing loss of voltage at the lamps (reducing light output) and causing heat within the switch, eventually destroying it if you're unlucky. Relays are cheap and do a better job of handling larger currents.

Separate relays for diffrent parts of the system also allows you to run diffrent parts of the system of diffrent fuses. Nice to not loose both headlights at the same time when driving at night...

 

Any voltage drop will reduce output of a headlight bulb right off a cliff. Relays work great but they aren't a substitute for poor grounds, connections, corroded cables and firewall block connectors etc. Voltage drop can be severe because of this as it's a long signal path from battery to ignition switch, down to floor switch, and then back out to headlights. Every terminal or connection loss of voltage is cumulative. Get the voltage drop minimized first, and then the relays will work all that much better.