Converting a 6-Volt Jeep to 12-Volt

by Eric Lawson


In early vehicles, the standard electrical system voltage was 6 volts. As long as you are willing to adequately maintain the 6 volt electrical system and are not wanting to add much extra electrical equipment, it will work fine. Parts are still relatively easy to find provided one knows where to look.

I converted my Jeep to a 12 volt electrical system for two reasons. One was a need to install a high power commercial 2-way radio in the Jeep. The other reason came to light when I needed a jump start and no one could help me.

Note: Gary Dreyer found that the 6 volt system in his 1954 Willys fire truck was turning the engine too slowly. He says, "Because the upgrade to 12 volts was not cost effective (i.e. changing all lights, siren and tube-type radio, not to mention the regular changeover costs). I checked into 'other alternatives.' I ran into an oldtimer who suggested switching to an 8 volt battery. He stated that there was nothing else which needed to be changed. After doing a little more research I bought the 8 volt battery and the battery shop told me the advice was only partially correct, and that the voltage regulator needed to be adjusted. The cost for the total upgrade was the cost of the battery and $25 to get the voltage reg adjusted at the local electrical rebuild shop. Results: engine zips over like a 12 volt system, lights are brighter but not blowing, and the charging system actually shows charging with all acessories on."

If you are wanting to convert your CJ-3B from a 6 volt negative ground to a 12 volt negative ground electrical system, the task is not difficult, nor is it terribly time consuming. The negative ground means that the negative terminal of the battery connects to the Jeep's engine block, body or frame.

This is more of a set of notes about issues to be aware of before and during the conversion rather than an exact step by step procedure to complete the conversion. I've tried to be as exact as possible, but with any old vehicle, modifications make describing all possibilities a challenging task.

1953-54 dashThis page is fairly specific to the 1953-55 CJ-3Bs with the 4 gauges and a speedometer on the dash, not an instrument cluster. Because of the similarity of the early CJ-3B electrical system with earlier CJ Jeeps, most everything mentioned in this conversion applies to the earlier Jeeps as well. A short section at the end mentions those things in the conversion that are different about the CJ-2A and CJ-3A Jeeps.

There are also 6 volt CJ-5s, or later CJ-3Bs, with an instrument cluster (30K GIF), and instructions on converting the instrument cluster to 12 volts are not specifically included on this page.

Some Safety Tips

Most of these safety tips are obvious, but it seems that the obvious things are the ones that cause accidents.

Some other helpful tips:

As you disconnect wires mark them and draw a diagram showing where the wires were connected.

In the drawings that I have made I show the wires in several different colors. I use these colors to help clarify the text. THESE ARE NOT THE COLORS OF THE WIRES IN YOUR JEEP.

Take the 6 volt parts with you when you purchase the 12 volt parts. The parts that the parts manuals say should be used may not fit becauseof other modifications to your Jeep.

Keep notes on the part numbers of the parts that you have installed in your Jeep. Since your Jeep is no longer "factory stock",the parts manuals are no longer completely accurate. When you need replacement parts, the notes will make purchasing the correct parts much easier.

Getting Started

Remove the wire from the negative terminal of the battery, followed by the wire from the positive terminal of the battery, and remove the battery.

The Ignition System

In both figures 1 and 2, the light blue "wire" is the wire that comes out of the wire bundle that comes from the inside of the Jeep and the large gray "wire" is the high voltage spark plug wire.

Figures 1 and 2

If you look at the wiring to the ignition coil, you should see the wires arranged as shown in figure 1. Note that the ignition coil's terminals are marked with a "+" and "-" sign. The small wire from the distributor should connect to the ignition coil terminal that is marked with the "-" sign.

To operate properly some 12 volt ignition coils require the use of an external resistor. If your coil requires one, it should say "USE EXTERNAL RESISTOR" or something similar on the coil and on the coil's packaging. The ignition coil and resistor are matched to operate together. You should use only the resistor that is recommended by the ignition coil manufacturer.

Disconnect the wires from the 6 volt ignition coil and remove it. Install the new 12 volt ignition coil. If your new ignition coil does not require an external resistor, reconnect the wires as shown in figure1.

If your new ignition coil requires an external resistor, mount this resistor to he firewall and connect the wires as shown in figure 2. You will need to add the wire (shown in dark blue) between the ignition coil and the resistor.

The distributor, ignition points, condenser, spark plugs and ignition wires do not have to be changed when converting to 12 volts.

The Charging System

If you are going to install an alternator, remove both the 6 volt generator and 6 volt regulator, use a one wire alternator and follow the instructions for Installing an Alternator.

If you are going to use a 12 volt generator:

First, some information on the labeling of the regulator and generator terminals. This applies to both the 6 and 12 volt parts. The regulator has a "B", an "A", a "F" and aground terminal. The generator has an "A", a "F"and a ground terminal. These terminals may have slightly different names. "B" may be called "BAT" , "A" may be called "G" or "GEN" and "F" may becalled "FLD". The ground terminal on the generator is usually a tapped hole that is adjacent to the other two terminals. The ground connection on the regulator is one of the screws which hold the regulator onto the Jeep.

The wires connecting to the 6 volt regulator and generator will be as shown in figure 3. The positions of the terminals on the regulator and generator will most likely be different than I have shown in the drawing, so don't try to identify the terminals by their physical positions. If your 6 volt regulator or generator has any extra wires or components connected to its terminals, make sure these wires get reconnected to the proper terminals. The extra component you will encounter most often is an ignition condenser attached to the generator. The body of the condenser will be attached to the ground terminal of the generator and the condenser's wire will be attached to the A terminal of the generator. The condenser may have been installed after the Jeep left the factory to reduce the amount of static heard in an AM (medium wave broadcast) radio.

Figure 3: 6 volt generator wiring
Figure 3

If the 6 volt regulator and generator terminals are marked, your job will be much easier. If they are not marked, you will need to identify the B terminal on the regulator. The B terminal will be the one that has a wire leading to the ammeter.

Once the B terminal has been identified, the generator and regulator can be removed.

When you purchase the 12 volt generator, bring the 6 volt one with you to verify that the generator is the same size and so the generator pulley can be installed onto the new generator.

When you reconnect the wires to the new generator and regulator, the wires need to be connected to the similarly named terminals on the new parts. See figure 3. Again, the terminals on your generator and regulator may not be in the same positions as I show in the drawing.

When you are connecting the wires between the A, F and ground terminals of the generator and regulator, check the wire sizes. If one of the wires is smaller in diameter than the others, use the smaller wire to connect to the F terminals together. If the wires are all the same diameter this will not be an issue.

The generator will need to be polarized in order to work correctly, however this can not be done until after the battery is installed in the Jeep. If you do not polarize the generator before you start the engine you risk damaging the regulator. All of the generators commonly used in Jeeps use the same polarization procedures. Because you may have ended up with a different type of generator, it is a good idea to ask how to polarize your particular generator before you leave the parts store. If the instructions you receive from the store conflict with those included near the end of this article, follow the parts store's instructions.

The Starter

Remove the 6 volt starter and replace it with the 12 volt one. The 12 volt starter will have only one terminal, so reconnecting the wires to it will not be a problem.

On the advice of a friend, I retained the 6 volt starter. I have heard that some people have had problems with doing this and had to replace the starter and flywheel ring gear within a year of converting their Jeep to 12 volts. I converted my Jeep to 12 volts over 9 years ago and have not had any problems.

The 6 volt CJ-3Bs have a floor mounted starter switch and no solenoid. If you wish to gamble and retain the 6 volt starter after you have converted to 12 volts, you do not have to change any part of the starter system.

If you do change the starter, the starter switch does not have to be changed.

External Lights

Remove the two 6 volt headlamps and replace them with 12 volt units. The 12 volt lamps plug into the existing light sockets. The part number of the headlamps that I used was 6014.

Replace the front and rear signal lights with #1034 bulbs. No wiring changes are needed to accommodate the 12 volt bulbs.

If your turn signal switch has an indicator lamp in it, you will need to take the 6 volt lamp to the parts store to get a 12 volt equivalent. You will most likely need a #53 bulb, but there many other possibilities.

The last thing that will need to be replaced is the turn signal flasher. I ended up using a #550 flasher although a #524 flasher should work as well. My Jeep's wiring was nearly non existent, so I was rewiring the Jeep as I was converting to a 12 volt electrical system. Again, the best thing to do is to take the 6 volt flasher to the parts store and get a 12 volt equivalent. Both the 6 volt and 12 volt flasher terminals will be marked with X, L and P. The wires connect to the similarly labeled terminals on the 12 volt flasher.

Replace the headlight hi-beam indicator with a #53 bulb.

Replace the dash light with a #63 bulb.

The headlight high beam switch, the headlight switch, the brake light switch, the headlight circuit breaker and the turn signal fuse do not need to be changed when you convert to a 12 volt electrical system.

Some people might wonder about the fuse and circuit breaker remaining the same. The primary job of fuses and circuit breakers is to protect the wiring from damage caused by excessive current being drawn through the wiring. Since the wires are remaining the same, the fuses and circuit breakers can remain the same.

See also a 1957 Owner's Manual Insert with 6-volt and 12-volt Bulb and Fuse Numbers.

The Instruments, Instrument Lights and Senders

Replace the 6 volt fuel gauge and fuel gauge sender with the equivalent 12 volt parts. I used a VDO fuel gauge and sender as the 12 volt replacement. Their fuel gauge sender has the same mounting hole pattern as the Jeep's fuel gauge sender. I believe the 6 volt sender's mounting hole pattern is the modern standard so other instrument companies' gauges should work too.

The VDO sender's length is adjustable, but its apparent shortest length was longer than the length recommended for the Jeep's gas tank. This confused me until I realized that this sender was designed so it could be cut to the proper length and then reassembled.

Follow the wiring instructions that come with the 12 volt fuel gauge. If the instructions refer to 12 volts or to a wire connected to the ignition circuit, this will be the wire that comes from the ignition switch. The 12 volt fuel gauge that I used had three terminals marked with + , S, and a ground ground symbol. The wire coming from the ignition switch connected to the + terminal and the wire coming from the sender connected to the S terminalon the fuel gauge. The wire from the terminal marked with the ground symbol needs to be connected to a point that is grounded, such as a bolt that mounts something to the firewall.

The ammeter and speedometer, oil pressure and temperature gauges do not need to be replaced.

Horn, Heater and Battery

The horn must be replaced with a 12 volt version. The horn in the CJ-3B has two wire terminals, so your 12 volt horn must also have two terminals. When reconnecting the wires to the new horn, it does not matter which horn wire connects to a particular horn terminal.

Heater Motor

Since the heater motor in a CJ-3B is a single speed motor, the easiest approach for converting it to 12 volt operation is to get a voltage dropping resistor. I don't know the part number or manufacturer of the needed part. To get the right part, tell the person at the parts store that you need a dropping resistor to run a 5 amp, 6 volt heater motor on a 12 volt electrical system. This will provide enough information to get the correct part. The dropping resistor gets warm during operation and most of these resistors depend on being mounted to the firewall to prevent them from overheating.

This part is not the easiest thing to find in the newer auto parts stores. You'll probably have better luck finding the dropping resistor in a parts store that has been in business for 20 or 30 years and has experienced counter personnel.

To wire the dropping resistor in place, disconnect either wire from the heater switch and connect the wire to one terminal of the dropping resistor. Then run an additional wire from the other terminal of the dropping resistor to the now empty terminal on the heater switch.


Replace the 6 volt battery with a 12 volt one. On my Jeep, the battery hold down clamp is a wire frame that sits on top of the battery. Long bolts come up through the battery tray and hold the wire frame down tightly against the top of the battery. I had to cut the wire frame in four places and have it rewelded so it would fit correctly onthe new battery.

Connect the positive battery cable to the positive terminal of the battery.


If you are like me, and are not so brave, use a test lamp during the initial checkout. The test lamp will prevent damage to the wiring should there be any problems. Connect a wire from the negative terminal of the battery to one terminal of a two terminal (single filament) 12 volt headlamp and then connect a wire from the other terminal of the headlamp to the Jeep's body. The negative battery cable is not connected.

This "test lamp" performs two functions.

Unfortunately the test lamp limits the ability of the electrical system to operate the electrical accessories in the Jeep. The test lamp will cause the accessories to operate as if the batttery was nearly discharged.

During these tests, the test lamp will only dimly light or not light at all. The exceptions to this "rule" are when cranking the starter and testing the headlight wiring. During these two tests, the test lamp will light fairly brightly.

If the test lamp unexpectedly lights to full brightness, you should check for short circuits in the wiring leading to the part of theelectrical system that you are testing.

  1. With everything off in the Jeep, the test lamp should not be lit. If the test lamp is lit, you have a short circuit somewhere that needs to be corrected. The most likely place to check will be the regulator/generator connections. The second place to check would be the wiring to the starter.
  2. Turn the ignition switch to the "run" position. Most of the tests will need to be performed with the ignition switch in the "run" position.
  3. If you have any gas in the tank, the gas gauge should move upward.If you remove the wire from the gas gauge sender and touch to the Jeep'sbody, the gas gauge should move to Full. With this wire not touching anything, the gauge should read empty. Don't forget to reconnect the wire to the fuel gauge sender.
  4. Press the brake pedal. The brake lights should dimly light up.
  5. Try the turn signals -- both directions. The turn signal lights may not flash, but they should at least light up. If the test lamp does not light to full brightness continue testing the rest of the Jeep's electrical system. The turn signals can be fully tested when the negative battery cable is connected to the negative terminal of the battery. Return the turn signal switch to the center position.
  6. Try the parking lights. The parking lamps and the dash light illuminating the instruments should dimly light up.
  7. Try the low beam headlights. They should light dimly light up.
  8. Try the high beam headlights. They should light up, but will be very dim. The high beam indicator lamp should also be lit, but it may be so dim that it will be difficult to see.
  9. Turn the headlight switch off.
  10. Try the horn -- it should at least "try" to sound.
  11. Try the heater motor . It should turn slowly. Turn the heater off.
  12. Turn the ignition switch off.
  13. Make sure everything in the Jeep is turned off, remove the test headlight and the test wires.
  14. Double check the regulator and generator connections. Be especially certain that these wires are correctly connected. This is the most likely place to make a mistake and any mistakes here could damage the regulator or generator.
  15. Connect the negative battery cable.

Generator Polarization

Alternators do not need polarization. DO NOT ATTEMPT TO POLARIZE AN ALTERNATOR.

If the polarization instructions you received from the generator supplier are different from those listed below, follow their instructions and ignore the ones listed below.

To polarize the standard Delco or Autolite generators that are normally used on the Jeep, use a jumper wire to momentarily connect the B to the A terminal (terminals 1 and 2 in figure 3) on the regulator. A second is all that the jumper should be left in place. You will get a spark when you connect the two terminals together -- this is normal.

Final Notes

The engine should start.

The ammeter should indicate the battery is being charged. If not, turn the engine off and leave the headlights on for a few minutes. This will discharge the battery enough that the ammeter should show charging when the engine is started. If the ammeter still does not show charging, check the wiring to the generator. To check this further, see the generator troubleshooting section.

If the starter cranks the engine, but the engine won't start, check the connections to the ignition coil and, if it is used, the external resistor.

If the turn signals did not flash before, try them now.

Notes for CJ-2A and CJ-3A Jeeps

Eric's CJ-3AThese instructions for the CJ-3B apply exactly to a CJ-2A or CJ-3A that has had an aftermarket turn signal system installed. If your CJ-2A or CJ-3A still does not have turn signals, replace the front parking lights with #67 bulbs and ignore the instructions relating to modifying the turn signal system. All of the other CJ-3B instructions will apply.

-- Eric Lawson


Thanks to Eric for this Tech Tip page. The photo above shows Eric's CJ-3A (with front clip from an M38). -- Derek Redmond

See also CJ-3B wiring diagrams on the Parts Illustrations page.

Return to Installing an Alternator, or see other Tech Tips on CJ3B.info.

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Last updated 26 November 2004 by Derek Redmond redmond@queensu.ca
All content not credited and previously copyright, is copyright Derek Redmond