6V to 12V conversion advice

JMFL36

JMFL36

Senior Member
I recently acquired a '54 Merc that the previous owner had converted to 12V with an alternator. Motor runs fine. It looks like he also changed out all the bulbs. I started probing the car with my multimeter today and it appears no 12-to-6V reducers were installed, as I am getting nearly 12V at the dash gauges, clock, radio, horn and heater blower power leads. The car also has power windows and seats which I have not probed yet, although I suspect I'll find the same results. Some of the gauges work, some don't. The clock, horn, and radio don't work. The windows and seats work but seem to operate faster than normal.

Would you suggest putting in individual reducers at each accessory? Or putting in one reducer to convert all circuits (except ignition and lighting) to 6V? Or something else?
 
My avatar was 12V when I got it. Dash lights are fine. It has no reducers but the radio is not hooked up. The heater motor runs fine but at a higher rpm-wires, motor and switch do not run hot. I would not do anything unless you suspect PO had problems. Of course maybe I have been lucky!!
 
I knew a guy who had a '54 Ford glasstop, 2-dr hardtop which he had converted to 12-volts. He did not change the power seat motor, nor any of the power window motors and also left the 6-volt starter intact. These motors never see anything more than short-term intermittent use, thus they are not harmed, but they do run faster. However, the heater blower motor is continuous duty, therefore, he installed a '56 Ford 12v motor. You cannot run the original clock, radio or other accessories without a 6-12v conversion, or use a 6-volt resistor ahead of the circuit. Wiring can remain as is because the 6-volt wire is often heavier. Light switch is okay as is also for same reason. All lamps need to be changed to 12 volt. As far a gauges, I am not familiar with what system the Mercury cars used, so someone else will need to reply about that.
 
I would note that the power window and power seat motors operate via a relay. The contacts in the relay which complete the circuit when the relay coil is tripped on would be okay for same reason as light switch and other switch contacts are twice as heavy as they need to be for 12 volt current. (As voltage increases, amperage decreases in comparison between operating the same load). However, I am not sure if the relay coil itself can withstand the increased voltage without affecting the life of the coil. At least it is a short-term intermittent load, which helps.
 
The 6 volt seat motors, relays, and horns have been running 15+ years in my bird on 12 volts. Just don’t run them continuously. The clock and radio, being positive ground, I’m not sure just a reducer does it. My clock never worked, and the radio was a conversion when I bought the car.
 
miker98038 said:
The clock and radio, being positive ground, I’m not sure just a reducer does it.
Click to expand...
No, they would need and 6-volt reducer AND a polarity inverter. I would recommend not buying one as they are made in China now and at best only last a couple months. Waste of money. On top of that, who's to say the old clock and radio are in working condition anyway.
If you have already converted to 12-volts, you can get your clock converted to quartz movement by any number of auto instrument repair/rebuilders and it will not need a resistor nor inverter.
The radio can be gutted and outfitted with solid-state AM/FM stereo receiver also but it is very pricey. Many outfits do that conversion also.
 
Were the battery cables also swapped to Negative ground, or is it still Positive ground?
If the car has its original ignition coil the polarity should be checked, and there should be a ballast resistor (example photos below) wired in series with the "+" / Ign switch side of the coil. (if the car is now negative ground)

The info at this link was written for 6v '55 T-Birds but much of it will apply to your '54 Merc.
https://www.ctci.org/gilsgarage/6to12.php

A 6v positive ground clock will fry itself on 12 volts or in a negative ground system.
It may have a polarity selector tab on the back but would need a voltage reducer if it still works.
.
 

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Thanks guys for the tips. Here's the answers to your questions.

Negative ground:
Yes, the car was switched to negative ground. Yes, there is a ballast on the coil (see photo).

Clock:
I have not pulled the clock yet or checked its in-line fuse. Will let you know what I find when I do.

Radio:
The radio looks original (tubes) and does not work. I wired it to another 6V car battery and got nothing. The radio wiring in the Merc had a ceramic style reducer in the power line, but when I probed it I got 12V on both sides so it must be shorted. I'll probably just reinstall it and cap the power line for now. May look into having it rebuilt with modern innards down the line. Another have a favorite vendor for this?

Gauges:
The temp and gas gauges work and seem to be fairly accurate so I may leave them alone. The oil gauge's needle moves from 0 to past 80 (max) when I start the car. I'm going to try a resistor on its power line to see if it comes down. I plan on using this - https://www.speedwaymotors.com/Speedway-Runtz-12-Volt-to-6-Volt-Voltage-Reducer,2374.html

Seat and windows:
They all work so I think I'll leave them as is for now. I don't move the seat very often and the windows stay down most of the time here in Florida.

Heater/Vent blower:
It works so I'm going to leave it as is for now. Will replace with a 12V motor if and when the 6V motor gives up.

Horns:
I'm going to have to troubleshoot why the horns don't work. Was hoping it might just be a simple 6-to-12V thing, but from what you guys said I guess that's not it. Will report back when I find out more.

PS. I also added a photo of the car I'm working on.

Thanks, John
 

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I would use the Runtz type CVRs on the gauges that are available from 5th Avenue Internet Garage. Some folks like the single chopper type CVRs that were used in the early 12-volt cars up into the 60s but they are NOT a CVR. The voltage is all over the place with those units. With the modern solid state CVRs they regulate the voltage to exactly what they are rated for. Most of the Ford instruments were made by King Seeley clear up into the early 60s. Modern 12-volt gauges and senders could be altered to work if necessary.

The old 6-volt tube type radios still had a ******** coil unit in them to step up the voltage. These were not solid state yet so they are not polarity sensitive. Some of the old units may have had a solid state pulse DC units installed to repair them and they are polarity sensitive but most modern ones are negative ground.

Randy Rundle has a lot of the stuff needed for conversion to 12-volt on his web site.
 
JMFL36 said:
...
Gauges:
The temp and gas gauges work and seem to be fairly accurate so I may leave them alone. The oil gauge's needle moves from 0 to past 80 (max) when I start the car. I'm going to try a resistor on its power line to see if it comes down. ...
Click to expand...
Beautiful car!!!

If the Fuel and Temp gauges are working correctly praise the automotive gods, then leave them alone.
High oil pressure reading? Make sure it's correct or not before fixing it. Esp when the engine is cold and if you're using straight 30 or 40 weight oil.

If the engine starts up easily when cold that's good, if it struggles a little bit to catch & run there is an ignition wiring change that began in '56 to help them start easier.
 
FWIW, when you get to the radio. I’ve had several custom auto sound units. They seem to make one for your car. They work reasonably well if you’re not an audiophile. Mine are a bit hard to read the dial on, and I’ve had a couple fail in not too many years. I’m not saying don’t buy one, but in the long run they’re not my favorite.

The vendors that convert the radios can be pretty pricey depending on what features and power levels you want. Just google it when the time comes and several will come up.

Yours is a more rare car, for the stock look a conversion will probably be your best bet.

Nice car. Still got the 256?
 
Sorry, but the specialist that did the solid-state AM/FM conversion of my '55 Ford car radio went out of business long, long ago. He was one busy guy with stuff coming in from all over the country. Way too expensive though.
 
If you ask me, the only really good reason to do a 6-12v conversion is so you can have a modern AM/FM stereo in your car. That's why I converted my '55 Courier, just for the radio.
BUT, then you get in trouble with other stuff like gauges and temperature sending unit selection and clock conversions. You might get away with having the clock converted to quartz (specifying that it needs to work with 12V, negative ground system).
 
Am I crazy to maybe convert it back to all 6V? Given the Sun Valley is pretty rare, maybe it would be better to be original spec?

miker98038, yes it still sports its original 256.
 
No reason you can’t convert it back, 6 volt cars ran fine for years, many still do. You’ll be on the hook for a generator and some other parts, but not ridiculously priced.

If the car was rewired for 12 v that’s another question. 6 volt wiring carries twice the amperage, so the common 12 volt kits don’t have large enough wire. I’ve worked on a lot of mid 50’s cars, and have yet to see one where the original wiring insulation wasn’t brittle and starting to crack. I’ve seen a couple fires from that, minor ones fortunately. So you might have a look at the original wiring, and any changes and additions, or repairs. Under the dash looks better than under the hood, but may be just as likely to crack if you start moving the wires around.

So it depends where you’re going. If the car’s as nice as the pictures show, it’s probably worth more restored than modified, and a return to 6 volts and necessary factory wiring replacement helps that.

These guys might be able to help with the clock and radio either way. I don’t know them, so check them out.

http://dandmrestoration.com/
 
Several companies offer original type 6-volt wiring harnesses that have the correct gauge wire. Rhode Island, Narragansett, and Tyree Harris among others. On bulbs, you just need to know the 6-volt equivalents to fit the sockets. All that stuff is still available.
 
I wouldn't say you're crazy to convert it back :)! My battery cables were garbage when i got my car (on an 8-volt battery no less due to PO not bothering to address the real problem), i put new heavy gauge cables ( i think #00 - huge gauge to handle the amps) and its never given me a problem since. My '55 always starts/runs on 6v and actually starts better than my 81 pickup (12v). go figure. I may just be lucky, but i've (thankfully) never had a reason to convert to 12v.
 
The most complaints I always hear about the 6-volt system is the starter/battery. I know people who have converted to 12-volts just for that reason. My '55 was a weak starter for decades till I finally got a brand new reproduction starter and the right size battery cables. Never had a problem starting since (as long as battery was okay).
Cars had 6-volt electrical systems from the early days up until '56. The only reason why the manufacturers switched to 12-volts is because the wiring doesn't need to be as large for a 12-volt system. (the higher the voltage, the lower the amperage). Thus they saved tons of dough on copper.
Bottom line; if the car has all the proper components compatible with design, in good working condition, there is no problem. That argument holds true for the Load-o-matic advance system too (which I have heard too many dismiss as junk). They are junk only if the vacuum advance diaphragm is cracked or something in the carb is not working properly with it. But they are excellent if they are working properly.
 
As far as the horns go, if you want to keep it 12-volt, you can get repro 12-volt horns like the old Spartan horns. I think one of the repro parts suppliers also sells repro 6-volt Spartan style horns and they give a little discount if you buy them in "Hi and Lo" pairs.
I would also suggest replacing the horn relay if you are going to keep it 12-volts.
The weird thing about the way the horns operate (at least it was this way on the Ford's), is that all the power wiring is connected un-switched. The horn button contact at the hub of the steering wheel completes the circuit when the horn ring is pushed. That wire is actually the horn ground wire.
 
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