6 to 12 Volt Conversion - 1955 Ford

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There are a number of guides on the internet.  They are mostly very good, but in case they don't have something you need, here also is my experience.  I converted my car in 2003, and have driven it over 20,000 miles since then ... so I think the conversion is a success :-)

If you have an average car with no special accessories, this is basically a pleasant (haha) weekend project.  I was lazy and my car was down a whole month, but that should not be necessary.  This is for a basic car.  If you have power seats, power windows, overdrive, or some item not covered here, I can't help you on those.  It should go without saying you need all your parts and everything mapped out before you begin.  You can't just do it a little at a time, and drive as you convert!

(1) Wiring.  If your wiring is in good condition, everything can be used without modification.  50-year old wiring is usually cracked and would need replacing anyway.  But if it's OK, there's nothing inherent in the wiring that makes it unsuitable for 12 volts.  In fact, 12 volt can actually use SMALLER diameter wiring than 6 volt.

(2) 12-volt battery .  Make sure it will fit.  Reverse the cables so you will have negative ground.  You may need new cables to accommodate.

(3) 12-volt generator & regulator.  They are the same from 1956 to 1964, on all Ford Y-blocks. (I believe no Y-block ever came with an alternator new.)  Generator and regulator are the same for either Y-block or FE.  Also the same for 223 six, except on the generator, the Ground and Field terminal posts are rotated to a different position on the generator body.  Even so, it bolts on interchangeably and I have used either generator on either engine, V8 or 6-cyl.  Generator & regulator are setup the same whether 12 or 6 volts, you wire them in the same way.  NOTE ... I would advise you to do away with the generator and regulator altogether and go with a modern alternator.  More on that later.

(4) 12-volt coil.  The coil is the only item on the car that is polarity-sensitive.  When you replace the coil, reverse the leads.  On Ford factory coils, the terminals are marked "Ignition" and "Distributor".  Other coils are marked "Pos" and "Neg".  Positive now goes to ignition (i.e., 12-volt power) and Negative goes to the distributor.

(5) Ballast resistor.  6 volt cars do not have a ballast resistor.  It was added in 1956, when Ford adopted 12 volts, to protect the points from the new higher voltage.  I have heard some old-timers say the ballast resistor cuts the voltage in half, so the points will continue to receive 6 volts as before.  Actually that is not true, it drops only a few volts, so with a 12-volt system (actually running closer to 14 volts), with a ballast resistor of the correct rating, the points will still be getting around 11 volts, rather than 7.5 as before.  For 1956 the ballast resistor was mounted standing upright on the coil rear mounting bolt.  That was not one of Ford's better ideas, as it seriously interferes with access to the distributor when you have to adjust points.  Beginning in 1957, the ballast resistor was moved to the driver's side firewall, away from the distributor and I highly recommend that position for your '55.  You'll have to drill a little hole for the screw.  Make sure it doesn't interfere with the linkage or anything on the other side of the firewall.  Cut the wire that leads to the Positive side of the coil, and wire the resistor inline.

(6) Solenoid.  You will need a new 12-volt starter solenoid.  Ford 12-volt solenoids were the same beginning 1956 up until at least the early seventies.  The extra little terminal on top is to be wired to the Positive side of the coil.  This gives full voltage to the points (without going thru the resistor), ensuring hot as possible spark during starting cycle only. 

(7) Starter motor.  The starter motor does not have to be changed or modified, or touched.  Just leave it as is and do nothing.  Switching polarity on the car does not reverse the direction the starter motor turns.  If you don't believe me, remove and test it both ways.  Better yet, don't waste your time, many people have already tested it, including myself.  If you eventually want to change over, 12-volt starter motors are all the same for all Y-blocks (272-292-312) 1956 and later.  (I think they are the same starter motor for 223 6-cyl, Y-block, and 332-352 FE, but I am not absolutely positive about that.)  Please see the article at the end of this Guide for information about the starter.

(8) Horns.  Use any 12-volt horns, but be aware the two holes on the mounting bracket probably won't line up.  I used Ford Mustang horns from the 1960's.  I had to move the horns anyway when I installed A/C.  They are mounted securely with one Grade 8 bolt each as I wasn't in the mood to drill new holes that particular day.  

(9) Horn Relay.  You will need a 12-volt horn relay.  The 1956 Ford 12-volt horn relay looks the same as the 1955 6-volt version.  If you can't find one, you can get a generic horn relay from the auto parts store.   

(10) Light bulbs.  Label all the light bulbs with masking tape as you pull them.  Otherwise you'll have trouble figuring out what goes where later.  These are all common bulbs, and everything has a 12-volt counterpart at the auto parts store.  Pay careful attention in the instrument panel.  There are a lot of little bulbs, and some of them are different shapes;  don't mix them up.  Make sure you get all the lights.  There are headlights, parking lights, taillights, backup lights, license plate light, dome light, instrument panel lights (I'll try to map them later), heater control light, radio light, clock light.  Messing around with light bulbs behind the instrument panel is probably the most difficult part of this whole project.

(11) Flasher.  The flasher on this car is an odd-looking little rectangular doo-dad clipped onto the inner dash near the ignition switch.  Replace it with the common cylindrical two-pole 12-volt flasher you find at any auto parts store.

(12) Heater motor.  Use a heater motor from a 1956 or 1957 Ford.  You may have to switch out the mounting plate and/or the squirrel cage fan, if it doesn't clear the housing.  It is not a big deal.  You will need an Allen wrench.  I thought the fan would be permanently seized on the motor shaft, but surprisingly, it loosened easily and everything came apart with no problem. 

(13) Instrument voltage regulator.  Instrument gauges (gas and temperature) are wired directly to 6-volt auxiliary supply.  After your 12 volt conversion they will still need to receive only 6-8 volts.  I do NOT recommend Runtz Resistors, little electronic gadgets made for this purpose.  They are expensive, you need one for each gauge, and they fail in a very impolite way.  You would think if the resistor fails, the gauge would then get zero volts, correct?  That would be inconvenient to be sure, but at least safe for the gauges.  No, when the Runtz Resistor fails, it just starts letting full voltage through.  So the gauge immediately starts getting 12-14 volts, rather than 6-8 it was designed for.  If you want that, go ahead and buy Runtz Resistors.  I say, just do what Ford did in 1956.  Even after 12-volt systems were introduced, Ford retained the 6-volt gauges for many years, up into the 1970's.  They made a voltage-drop "regulator" which is exactly what you need.  Get it from a Mustang dealer, or search Ebay for "Ford Instrument Regulator".  Now, it does not just simply put out 6 volts.  If you connect everything and then test output with a voltmeter, you won't get a steady 6 volts.  You'll get readings all over the place, jumping from 0 to 13 and everything inbetween.  This is because the regulator doesn't put out one steady voltage, it pulses between open and closed, giving an "average" of 6-8 volts which keeps the gauges happy.  You only need one such regulator, and branch output to both gauges.  Also, don't just leave it hanging -- it MUST be mounted on "ground" in order to work.  I have it bolted on the stationary brace above the brake pedal.

(14).  Gas gauge.  You don't have to worry about polarity of the gas gauge, and you don't need a new sending unit.  After you have installed the instrument voltage regulator described above, you are done.

(15) Temperature gauge.  As with the gas gauge, you need the original 6v sending unit and the original gauge, wired from the instrument voltage regulator described above.  As with the gas gauge, the current travels from 12v auxiliary power, into the instrument voltage regulator, then at reduced voltage into the gauge, then into the sending unit, and thence into ground (I know, it doesn't sound like the right order).  

(16) Headlight switch.  This doesn't have to be changed, neither does any other simple on/off switch on the car.  Be aware, however, the instrument dimmer rheostat will not have much effectiveness.  You can get full on and full off, but not much range inbetween.

(17) Lighter.  There is no need to change the receptacle, but be aware the lighter element is definitely a 6-volt unit.  If used on the 12-volt system, it will get hot very quickly and pop out forcefully (actually comes flying out of the receptacle).  I wouldn't advise doing this very often.  Surely you don't smoke in your 60-year-old limousine.

(18) Radio.  Please don't connect your radio to 12 volts, or be tempted to mess with a voltage-reducing resistor.  The radio needs to be professionally rebuilt.  Mine was done by Ebay user "DBCUDA" --highly recommended.

(19) Clock.  I've been informed by clock rebuilders that 6-volt electrical clocks can be run on 12 volts, since the winding mechanism is engaged for only a split-second at a time.  Just make sure it has its own fuse.  Reversing polarity is also not a problem.  If you are uncomfortable with that you could just get a wind-up version.  1955 was the last year for Ford wind-up clocks.  Either clock will still need a 12-volt bulb.

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Miscellaneous FAQ's

Q.  What happens if I forget to switch a lightbulb?

A.  It will burn superbright for a minute or two and then burn out.

Q.  How can you get away with not changing the starter motor?  Why does it not change direction when polarity is reversed?  Electric radiator fans definitely change direction when polarity is reversed.

A.  First off the starter motor is a very heavy duty electric motor, designed for intermittent use only, and as such it can handle short bursts of 12-volts normal in starting.  I've been driving it that way for years now.  (Anyway I do carry an extra 12-volt starter motor in the trunk on long trips, along with several other parts in case I wish I had them.)  As to why it does not change direction:  both the armature and the field are wired, and when you change polarity you are changing BOTH armature and field.  Modern electric motors use permanent magnets as the field, so when you switch polarity you are only changing the armature, hence the direction change.  See attached technical article below. 

Q.  Oh what all parts do you carry in the trunk if I may ask?

A.  Starter motor;  points & condensor;  new water pump;  new fuel pump;  spare carb;  one rear axle shaft w/ bearing (from a 53 ... make sure they have the same number of splines ... same from 49 to early 55 only);  rear axle seal;  spare generator & regulator (before I went to GM alternator);  dwell meter and a few basic tools.  Also used to carry a pair of exhaust manifolds when I was even more paranoid than I am now.

Q.  Running 12-volts thru existing 6-volt wiring is dangerous and a fire hazard.  The wiring has to be twice the size as for 6-volt.

A.  No, that is not correct.  Actually it is the other way around.

Q.  What about the 6-volt points and condensor, and all the switches, the ignition switch, the door jamb light switches, the headlight dimmer switch, the sending units, the heater switch etc.??

A.  You don't need to replace them.  They are not specific to either 6 or 12 volts. 

Q.  My brother-in-law, who is an electrician, says "__________________________" (fill in the blank).

A.  Follow whatever your brother-in-law says.  I believe the information in this guide is correct.  If not, please let me know. 

Q.  What about the wiper motor?

A.  If you have electric wiper motors, they would have to be changed.  I do not believe there was ever such a thing on a 1955 Ford.

Q.  How about using voltage-drop resistors for the heater motor etc.

A.  Those resistors run hot.  You are pulling the same power but half of it now is being converted to heat, pointlessly.  You have to drill holes to mount the resistors on sheet metal, as a heat sink.  That looks ugly.  And also, most people (including me) don't know the formula for what type or how many resistors are necessary.  And why bother anyway?  The later motors fit your heater housing exactly.   

Q.  If you maintain a 6-volt car, it will run fine forever.  They ran fine in 1955, and they will still run fine on 6 volts.

A.  Fine, just don't break down in my lane of traffic during rush hour on the 880.

Q.  1955 Chevies are better than 1955 Fords because they already had 12-volt from the factory.

A.  Yeah, but the problem is, they look like they are chewing lemons.

Q.  What happens if you reverse polarity on the horns?

A.  Then they no longer blow, they suck :-)

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Why Doesn't the Starter Motor Turn the Opposite Direction When Polarity is Reversed?

Technical information submitted by David Dare (Ebay ID:  simplyconnected )

Direct Current Motors have two basic components, the stationary Field poles (which produce magnetism) and the rotating Armature (which also produces magnetism).  The Armature uses brushes so it can always be in the optimum position for the strongest magnetic pull, causing the motor shaft to turn.

Armatures and Fields are wired in one of three ways, and I am DEFERRING permanent magnet field motors until later.  These are all used for different applications.

Series Field:  This wiring method produces the STRONGEST starting torque, but poor speed regulation.  The armature is wired in series with the field wires, which means the field wires have to carry the same current as the armature (VERY heavy field wires, lots of current makes lots of magnetism, creating lots of torque).

Shunt Field:  The armature is wired in parallel with the field.  Very small field wires (and many more turns), great for speed regulation, but poor starting torque and really dangerous for 'runaway' if you open the field while the motor is running.

Compound Field:  A combination of both series AND shunt windings  This is the best all-around arrangement for good starting torque and fine speed control.

Ok, down to the nitty-gritty.  If you want to reverse the direction of ANY of these motors, just reverse either the Armature leads (A1 & A2) OR the Field leads (S1 & S2).

Note: On a Compound Motor, just reverse A1 & A2 because you don't want the two fields 'bucking' each other..

If you reverse BOTH the Armature AND the Field leads, the motor won't change direction.  So, there is a relationship between the direction of magnetism of the Field to the direction of magnetism of the Armature.  The direction of current always determines the north-south polarity of coil magnetism.

What is an automotive Starter Motor?  It is a Series Motor (for the greatest starting torque.  We couldn't care less about speed control).

And what do you see, looking at the outside of the starter motor?  First, you only get to see ONE heavy terminal; the other leads are already attached internally (one is connected to GND), right?  If you reversed the polarity, the direction will not change because you just changed polarity for both the Armature and the Field wires.

***PERMANENT MAGNET MOTORS***:  All the rules just changed (sort of).  We use rare earth and other very efficient materials to make great magnets, today.  (They didn't have that for serious motors in the old days; only little motors with weak magnets.)

Since permanent magnetism is constantly produced (not wired), if you change the polarity (motor leads), the motor will run in reverse!

All the NEW STARTER MOTORS USE PERMANENT MAGNETS!!!  This only started around 1993 or so.  That's why the starters got a lot smaller in size; the magnets are a lot smaller than the field windings were, so they used some of the space-savings to install gear reduction, for yet more torque.

THESE MOTORS WILL RUN BACKWARDS, if you reverse Armature polarity.  If you turn the magnets around, the Armatures will pull in the opposite direction (just like reversing the field wires).

Car companies realized a great savings by going to permanent magnet motors.  They no longer have to wind field coils (there are none to buy, install, or break).  They use fewer electrical connections.  (Fewer things can go wrong.)  Magnets are a little expensive, but they can always tell the good ones from bad ones (for quality control), and they take up less motor space than field coils.)  I don't know if new starter motors are cheaper, but I know space savings is a big advantage.


Why Did Carmakers Use Negative or Positive Ground to Begin With?

As far as why they use positive or negative ground goes, the truth is, they couldn't make up their minds, and everyone went their own way.  One is just as good as the other.  Does current flow from positive to negative, or the other way?  They still argue that, but we all agree that everyone benefits from uniform standards.

The ignition coil polarity is another story, much like the motor story.  The coil is REALLY a DC Saturable Reactor.  If you wire it 'backwards' the resulting spark will go in the opposite direction (just like motor current).

Harley-Davidson has done this for many decades; they bang both spark plugs at the same time.  There is no rotor, or distributor cap; just a coil that is wired to two plugs.  While one cylinder is on its power stroke, the opposite cylinder is on its exhaust stroke.  Now, Ford does it too, starting with the Romeo 4.6L Engine.

To save cost, Ford considered putting platinum on only one spark plug electrode.  Since Direct Current runs through two plugs at the same time, one plug only needs platinum on its tip while the other plug needs platinum on its tang.  Ford ended up not doing it because of aftermarket confusion.  Platinum is very expensive.  Imagine the cost savings if you only used half the amount on each V-8.  (Romeo produces 1,500 engines each day.)

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