Changing your 6 volt vehicle to 12 volts by Al at AutoReWire.com

Converting from 6 volts to 12 volts is pretty straight forward. 

I get a lot of emails regarding this subject.  What I have done here is to provide you with a sort of road map to perform the conversion.  Obviously you will need a few parts and some supplies.  I have included links to the products that we normally keep in stock and have included links to others that supply products we don't stock.

If your wires are in good condition they will handle the 12 volts just fine as they are twice as heavy as they need to be.  The same is true of the switches in the vehicle.


GENERATOR  If you are keeping a generator you will need to replace both the generator and the voltage regulator with units for a '55 or later 12 volt model. 

If you are replacing the generator with an alternator I would suggest that you Google "replace generator with alternator" for a better understanding of what is involved.  I will outline below the most popular GM 10/12 SI alternator conversion.  I have also supplied links to Mark Hamilton's site as he does a great job of describing the reason for using a 3 wire instead of the popular 1 wire alternator.
  Other alternators will install similar to the GM.  More information is available on the web via your favorite search engine.

GM 10 or 12 SI ALTERNATOR - Most Popular Conversion

Remove the generator, voltage regulator and the wiring between the two.
  Mount a GM 10si or 12si alternator in place of the generator.  Universal brackets are available at most local Napa auto parts stores.  On most vehicles you can simply cut the appropriate lengths of 3/8" black iron pipe to make the spacers you need to install and align the alternator.  You may have to change pulleys if you have an older engine that uses a wide V belt (more info here).  For information on part numbers and case clocking
go here.

You will need to open up the wiring harness to do this if you haven't already.  We have 1" Non Adhesive Harness Tape available to properly re-wrap the harness here

Splice a 10 gauge wire onto the BAT wire that went to the voltage regulator and connect it to the BAT terminal on the GM alternator.  Don't go to the trouble of buying a 1 wire alternator unless you just want to get a chrome unit.   The factory 3 wire units will last longer and charge better.  For more info on this subject go here.

If you are using an ammeter in the dash DO NOT use an alternator larger than 63 amps and MAKE SURE that you install a 4 inch (minimum) length of  16 gauge fusible link between the alternator and the ammeter so that the gauge does not become the fuse in the circuit.  I like to install the fusible link at the alternator to keep it out of the passenger compartment and for ease of service if it should ever fail.  We have the Fusible Link Kits available.

If you have a dash indicator light splice a length of 20 or 18 gauge wire between the wire that went to the ARM on the voltage regulator and connect it to the # 1 terminal on the alternator. 
Go here for a drawing.  If you DO NOT  have a dash indicator light you will need to run a 20 or 18 gauge wire from the IGN switch to the # 1 terminal on the alternator and install a 10 Ohm 10 Watt resistor somewhere in that line in a place where it has good air circulation.  Failure to install this wire with the proper resistance will usually burn up the voltage regulator in the alternator.

It is best to run at least 36 inches of 12 gauge wire from the #2 terminal on the alternator to the BAT connector on the starter solenoid (or the fuse panel or the horn relay) as apposed to just jumping it as shown in my drawing.  If you read the Mark Hamilton article you will know why.

Another tip on Fusible Links.  GM designed the systems with the sensing splice in the harness and the 10 gauge system supply wire has a fusible link at the starter solenoid.  If you run the sensing wire to the starter solenoid you are smart to install a fusible link in it AND in the BAT charge wire.  The ROT (rule of thumb) is to use a fusible link that is four sizes smaller than the wire you are protecting.  So if you using a 10 gauge wire from the alternator to the starter solenoid then you would use a 4 to 6 inch length of 16 gauge fusible link.  12 gauge wire will need an 18 gauge fusible link.


STARTER...  Your existing 6 volt starter will work just fine for a long time if you do not crank it for long periods of time.  Of course cranking any starter for long periods will burn 'em up (as in throwing solder due to over heating) but the 12 volt driven 6 volt starter will get hot quicker and throw solder sooner that a 12 volt unit   Replace the starter solenoid with a 12 volt unit for a '55 or later model.  We have the early Ford style in stock.

COIL... You can use the original coil but you must install a new ballast resistor (1.2 to 1.8 Ohms) between the coil and the ignition switch.  I always test the coil output when I convert a car for a customer but it requires a special tester that most people don't have.  Anything over 30,000 volts is sufficient for a non performance engine.  You will need to reverse the polarity of the coil if your 6 volt systems was Positive ground as most were.  Wiring should run from IGN switch to one end of the ceramic resistor then from the other end of the resistor to the + post on the coil then from - post on coil to the points.   Points and condenser can be retained if they are in good condition.  If you need a new condenser, one for any 12 volt vehicle '55 or later that fits in the distributor will work. 

HORN RELAY... Replace the horn relay with a 12 volt unit.   Most 6 volt horns will work for a very long time on 12 volts, eventually you might need to change them to 12 volt units.  Most fan fair horns and some trumpet horns have an adjustment knob on the disc that you can adjust the tone with.  I wear ear protection when doing this, you should too.  We have some good USA manufactured units available.  Just give us a call or email...  They are plentiful at the local pull your own part wrecking yards too.

LIGHTS... Replace the headlamps and all of the light bulbs with new 12 volt units.  Yes this means you have to replace the ones in the dash that are sometimes very difficult to get to. Resistors and voltage reducers will not work properly DON'T BOTHER TRYING.

GAUGES...  Install one of our $3.00 (each) voltage reducers for each of your electrical dash gauges.  Not needed for the Ammeter.

HEATER ... Install a 1 Ohm ceramic reducer between the heater switch and the heater blower motor. 

WIPERS... If you have electric wipers you will need to install a 1.5 Ohm ceramic reducer between the switch and the motor.  The 1.5 Ohm resistor works best on the small wiper motors but we have found that some of the larger motors prefer the 1 Ohm.  If you are not sure I suggest that you purchase a 1 Ohm for the heater blower motor and try it on your wiper motor before you purchase the 1.5 ohm resistor.  With the motor running on the high speed you want to see somewhere between 6 and 7 volts at the motor.  If the motor is running too fast for your liking then I would suggest that you use the 1.5 ohm resistor.

TURN SIGNALS...  Change turn signal flasher to a 12 volt unit.  We have several different types in stock.

POWER SEAT and CONVERTIBLE TOP MOTORS...  Most will work fine with a 1 Ohm Ceramic Resistor others will need a pair of 1.5 Ohm Ceramic Resistors wired parallel to produce .75 Ohms.  Best way to test for what you need its to install a 1 Ohm and then check the voltage at the motor with it running.  It should be between 6.5 - 7.5 volts although something less will work without damage.  If the voltage is below 6 volts you might need to go to two 1.5 ohm resistors wired parallel.

RADIO... As for the radio, the best bet is to go to Custom Auto Sound and get a unit that will replace your original.

You could also have your 6 volt radio rebuilt to work on 12 volts.  Do a Google search on "
Antique Auto Radio" for more information.  For the D.I.Y. (do it yourselfer) who wants to "try" and make your original radio work on 12 volts read this and this.

CLOCK...  It is best to have a new quartz movement installed.  Do a Google Search on "Automotive Clock Quartz Conversion" for more info.

To purchase any of the above products please visit our Web Store or our Ebay Store.  If you can't find them in our stores we are temporarily out of stock.  You can call me at 209-481-6496 anytime 8am to 8pm Pacific time to order with a credit card or send me an email with your needs and I can send you a Paypal invoice.  International shipping is available.

Any and all comments are welcome.  If you feel something should be added please let me know.  Al@AutoReWire.com.