Converting a 6-Volt Jeep to 12-Volt

by Eric Lawson


In early vehicles, the standard electrical system voltage was 6volts. As long as you are willing to adequately maintain the 6 voltelectrical system and are not wanting to add much extra electricalequipment, it will work fine. Parts are still relatively easy to findprovided 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 theJeep. The other reason came to light when I needed a jump start and noone could help me.

Note: Gary Dreyer found that the 6 volt system in his 1954 Willys fire truckwas turning the engine too slowly. He says, "Because the upgrade to 12 voltswas not cost effective (i.e. changing all lights, siren and tube-type radio, not tomention the regular changeover costs). I checked into 'other alternatives.' Iran into an oldtimer who suggested switching to an 8 volt battery. He statedthat there was nothing else which needed to be changed. After doing a littlemore research I bought the 8 volt battery and the battery shop told me theadvice was only partially correct, and that the voltage regulator needed to beadjusted. The cost for the total upgrade was the cost of the battery and $25 toget 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, andthe charging system actually shows charging with all acessories on."

If you are wanting to convert your CJ-3B from a 6 volt negative groundto a 12 volt negative ground electrical system, the task is notdifficult, nor is it terribly time consuming. The negative ground meansthat the negative terminal of the battery connects to the Jeep's engineblock, body or frame.

This is more of a set of notes about issues to be aware of before andduring the conversion rather than an exact step by step procedure tocomplete the conversion. I've tried to be as exact as possible, butwith any old vehicle, modifications make describing all possibilities achallenging task.

1953-54 dashThis page is fairly specific to the 1953-55 CJ-3Bs with the4 gauges and a speedometer on the dash, not an instrumentcluster. Because of the similarity of the early CJ-3B electricalsystem with earlier CJ Jeeps, most everything mentioned in thisconversion applies to the earlier Jeeps as well. A short section at theend mentions those things in the conversion that are different about theCJ-2A and CJ-3A Jeeps.

There are also 6 volt CJ-5s, or later CJ-3Bs, with aninstrument 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 obviousthings are the ones that cause accidents.

Some other helpful tips:

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

In the drawings that I have made I show the wires in severaldifferent colors. I use these colors to help clarify the text. THESEARE 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 installedin your Jeep. Since your Jeep is no longer "factory stock",the parts manuals are no longer completely accurate. When you needreplacement parts, the notes will make purchasing the correct parts mucheasier.

Getting Started

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

The Ignition System

In both figures 1 and 2, the light blue "wire" is the wirethat comes out of the wire bundle that comes from the inside of the Jeepand 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 thewires arranged as shown in figure 1. Note that the ignition coil'sterminals are marked with a "+" and "-" sign. The small wire from the distributor should connect to the ignition coilterminal that is marked with the "-" sign.

To operate properly some 12 volt ignition coils require the use of anexternal resistor. If your coil requires one, it should say "USEEXTERNAL RESISTOR" or something similar on the coil and on thecoil's packaging. The ignition coil and resistor are matched to operatetogether. You should use only the resistor that is recommended by theignition 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 doesnot require an external resistor, reconnect the wires as shown in figure1.

If your new ignition coil requires an external resistor, mount thisresistor 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 ignitioncoil and the resistor.

The distributor, ignition points, condenser, spark plugs and ignitionwires 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 voltgenerator 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 andgenerator terminals. This applies to both the 6 and 12 volt parts. Theregulator 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 differentnames. "B" may be called "BAT" , "A" maybe called "G" or "GEN" and "F" may becalled "FLD". The ground terminal on the generator is usuallya tapped hole that is adjacent to the other two terminals. The groundconnection on the regulator is one of the screws which hold theregulator onto the Jeep.

The wires connecting to the 6 volt regulator and generator will be asshown in figure 3. The positions of the terminals on the regulator andgenerator will most likely be different than I have shown in thedrawing, so don't try to identify the terminals by their physicalpositions. If your 6 volt regulator or generator has any extra wiresor components connected to its terminals, make sure these wires getreconnected to the proper terminals. The extra component you willencounter most often is an ignition condenser attached to the generator. The body of the condenser will be attached to the ground terminal ofthe generator and the condenser's wire will be attached to the Aterminal of the generator. The condenser may have been installed afterthe 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 jobwill be much easier. If they are not marked, you will need to identifythe B terminal on the regulator. The B terminal will be the one thathas a wire leading to the ammeter.

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

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

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

When you are connecting the wires between the A, F and groundterminals of the generator and regulator, check the wire sizes. If oneof the wires is smaller in diameter than the others, use the smallerwire to connect to the F terminals together. If the wires are all thesame 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 theJeep. If you do not polarize the generator before you start the engineyou risk damaging the regulator. All of the generators commonly usedin Jeeps use the same polarization procedures. Because you may haveended up with a different type of generator, it is a good idea to askhow to polarize your particular generator before you leave the partsstore. If the instructions you receive from the store conflict withthose 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. The12 volt starter will have only one terminal, so reconnecting the wiresto it will not be a problem.

On the advice of a friend, I retained the 6 volt starter. I haveheard that some people have had problems with doing this and had toreplace the starter and flywheel ring gear within a year of convertingtheir Jeep to 12 volts. I converted my Jeep to 12 volts over 9 yearsago 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 haveconverted to 12 volts, you do not have to change any part of the startersystem.

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

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 numberof the headlamps that I used was 6014.

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

If your turn signal switch has an indicator lamp in it, you will needto 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 otherpossibilities.

The last thing that will need to be replaced is the turn signalflasher. I ended up using a #550 flasher although a #524 flasher shouldwork as well. My Jeep's wiring was nearly non existent, so I wasrewiring 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 partsstore and get a 12 volt equivalent. Both the 6 volt and 12 volt flasherterminals will be marked with X, L and P. The wires connect to thesimilarly 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 lightswitch, the headlight circuit breaker and the turn signal fuse do notneed to be changed when you convert to a 12 volt electrical system.

Some people might wonder about the fuse and circuit breaker remainingthe same. The primary job of fuses and circuit breakers are to protectthe wiring from damage caused by excessive current being drawn throughthe wiring. Since the wires are remaining the same, the fuses andcircuit 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 theequivalent 12 volt parts. I used a VDO fuel gauge and sender as the 12 voltreplacement. Their fuel gauge sender has the same mounting hole patternas the Jeep's fuel gauge sender. I believe the 6 volt sender's mountinghole pattern is the modern standard so other instrument companies'gauges should work too.

The VDO sender's length is adjustable, but its apparent shortestlength was longer than the length recommended for the Jeep's gas tank. This confused me until I realized that this sender was designed so itcould 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 theignition circuit, this will be the wire that comes from the ignitionswitch. The 12 volt fuel gauge that I used had three terminals markedwith + , 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 groundsymbol needs to be connected to a point that is grounded, such as a boltthat mounts something to the firewall.

The ammeter and speedometer, oil pressure and temperature gauges donot need to be replaced.

Horn, Heater and Battery

The horn must be replaced with a 12 volt version. The horn in theCJ-3B has two wire terminals, so your 12 volt horn must also have twoterminals. When reconnecting the wires to the new horn, it does notmatter 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 easiestapproach for converting it to 12 volt operation is to get a voltagedropping resistor. I don't know the part number or manufacturer of theneeded part. To get the right part, tell the person at the parts storethat you need a dropping resistor to run a 5 amp, 6 volt heater motor ona 12 volt electrical system. This will provide enough information toget the correct part. The dropping resistor gets warm during operationand most of these resistors depend on being mounted to the firewall toprevent them from overheating.

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

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


Replace the 6 volt battery with a 12 volt one. On my Jeep, thebattery 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 framedown tightly against the top of the battery. I had to cut the wireframe 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 thebattery.


If you are like me, and are not so brave, use a test lamp during theinitial checkout. The test lamp will prevent damage to the wiring shouldthere be any problems. Connect a wire from the negative terminal of thebattery to one terminal of a two terminal (single filament) 12 voltheadlamp and then connect a wire from the other terminal of the headlampto 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 electricalsystem to operate the electrical accessories in the Jeep. The testlamp will cause the accessories to operate as if the batttery wasnearly discharged.

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

If the test lamp unexpectedly lights to full brightness, you shouldcheck 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 needsto be corrected. The most likely place to check will be theregulator/generator connections. The second place to check would be thewiring to the starter.
  2. Turn the ignition switch to the "run" position. Most ofthe 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 touchinganything, the gauge should read empty. Don't forget to reconnect thewire 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 maynot flash, but they should at least light up. If the test lamp does notlight to full brightness continue testing the rest of the Jeep'selectrical system. The turn signals can be fully tested when thenegative battery cable is connected to the negative terminal of thebattery. Return the turn signal switch to the center position.
  6. Try the parking lights. The parking lamps and the dash lightilluminating 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 bevery dim. The high beam indicator lamp should also be lit, but it may sodim 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 testheadlight and the test wires.
  14. Double check the regulator and generator connections. Be especiallycertain that these wires are correctly connected. This is the mostlikely place to make a mistake and any mistakes here could damage theregulator or generator.
  15. Connect the negative battery cable.

Generator Polarization

Alternators do not need polarization. DO NOT ATTEMPT TO POLARIZE ANALTERNATOR.

If the polarization instructions you received from the generatorsupplier are different from those listed below, follow theirinstructions and ignore the ones listed below.

To polarize the standard Delco or Autolite generators that arenormally used on the Jeep, use a jumper wire to momentarily connect theB to the A terminal (terminals 1 and 2 in figure 3) on the regulator. Asecond is all that the jumper should be left in place. You will get aspark 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. Thiswill discharge the battery enough that the ammeter should show chargingwhen the engines is started. If the ammeter still does not showcharging, check the wiring to the generator. To check this further, seethe generator troubleshooting section.

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

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 thathas had an aftermarket turn signal system installed. If your CJ-2A orCJ-3A still does not have turn signals, replace the front parking lightswith #67 bulbs and ignore the instructions relating to modifying theturn 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.

FacebookVisit CJ3B.info on Facebook.

CJ3B Home | Contents | History | Photos | Tech | Toys | Links |Bulletin Board

Last updated 26 November 2004 by Derek Redmond redmond@queensu.ca