A 6v to 12v Conversion to Improve Your Car!

Changing over from 6v to 12v is one of the easier and cheaper projects to update an old car or truck. The benefits are easier starting and greatly improved headlights, as well as the ability to add 12v accessories.

However, before we get into this project, look over your wiring.

If your wiring is frayed, split, or cracked, start over. There is no sense putting all this work into changing over if you're still going to get shorts and take a chance on burning down the car. It's easier and cheaper to do it all once than to change over, fight bad wiring, have problems, then have to do it all over a second time...

Ok, let's get started...

First, if you're wiring and your switches are in good shape, then so are you!

A 6v wiring system and switches are more than enough to handle 12v. It's heavier because it has to carry more amperage. Less volts means more amperage. Changing to 12v cuts the amperage load approximately in half. So, the wiring will live happily with 12v.

Second, figure out if you have a positive or negative ground.

You will be going to a negative ground. So, if you have a positive ground, you need to do a few things first.

Start be reversing the power wires to anything that is polarity conscious. Things like the ignition coil, amp guage, wiper motor, heater motor, etc.

Also the battery cables will need to be changed or modified. The ground strap will need to reach and have the correct end to connect to the negative post and the cable to the starter solenoid will need to reach and have the correct end to connect to the positive post of the new battery.

Now, let's focus on the areas that you need to change.


The starter is usually the easiest area to deal with. 6V starters are just fine dealing with 12v and will last a long time.

You will need to change the starting solenoid over to a 12v solenoid. 6v solenoids will work if you need to start in an emergency, but will burn out quickly and could lock the starter on or cause a fire.

Usually 6v positive ground starters work just fine being switched over to 12v negative ground. Just change the cable to the positive battery terminal. However, you might find some models won't work and in that case take it to an auto electrical shop and have the motor leads reversed if you can't find a negative ground starter that will interchange. This is rare however.

Charging System

The first thing you need to do is get a 12v battery of course. Take your battery box measurements and get a battery that will work for your application. Also make sure you have clearance above if you use a top post.

Now you have the option to either switch to a 12v generator or a 12v alternator.

A generator isn't used as often, but it is simple to change out. The brackets are usually the same and wiring stays the same. You will have to change out the voltage regulator for a 12v one also.

Most choose to go with a 12v alternator. More specifically, most use a General Motors 10SI alternator. They're tough, small, and cheap, and most places have them in stock. They're also easy to wire in. They also do away with the stock voltage regulator as they already have an internal regulator. More info here: 10SI alternator info

They're not that hard to install as many brackets can be made or modified to install it. Many older 6 and 8 cylinder engines have brackets available that will work because later in life they switched to alternators. There are lots of aftermarket brackets available also. Check in any good hotrod or streetrod magazine for suppliers of brackets. Get creative!

To wire it in, unhook the wires from the voltage regulator, cut the ends and seal them off and tie them out of the way with the rest of the harness. Or you can remove them.

Now, using a 10 gauge wire, run from the Bat terminal on the alternator to the positive cable end on the starter. Or, if you have an ammeter in the dash, run from the alternator to it and then to the starter. Remember, you have to switch the leads on the ammeter if you're changing from positive ground to negative ground or it will read backwards.

Hook up another short 10 guage wire from the #2 pin on the alternator to the Bat terminal on the alternator. The #2 pin is the one farthest away from the Bat terminal. (You can get the plug for the 10SI alternator with the 2 wires from any auto parts store.)

Now hook up a 16 guage wire from the #1 pin on the alternator to an idiot light (a small light you can get from the auto parts store to put on the dash with 2 wires coming off of it.) Neither wire of the light goes to ground. Connect one wire to the 16 guage wire from the alternator, and the other to the ignition switch. Otherwise your engine may keep running after you shut it off. Now that's taken care of...


Your ignition system needs to be in good working order first. Plugs, plug wires, distributor cap and rotor, etc.

The first thing you want to deal with is the coil.

If you are 6v negative ground going to 12v negative, you can leave the wiring to the coil alone. If you are 6v positive ground going to 12v negative, you need to switch the two wires on the coil. Negative to positive, positive to negative. For a 12v negative system, the ignition switch wire goes to the + terminal on the coil. The wire from the distributor to the coil goes to the - terminal on the coil.

If you aren't going to use the car much and just drive it easy, you can get by with the old coil. You just have to add a ballast resistor to drop the voltage back down to 6v for the coil. We'll cover that in a minute.

If you are going to drive the car more and have some fun with it, switch to a 12v coil. They don't cost that much and are really recommended. They have more windings and live much better in a 12v environment. Some stock 12v coils need a ballast resistor and some don't. Here's some parts numbers for you:

-AC Delco part # U515
This is a universal 12v coil that DOES NOT need a ballast resistor.

-AC Delco part # U505
This is a universal 12v coil that NEEDS a ballast resistor.

Where would I put a ballast resistor?

You put it in the wire from the ignition switch to the coil. You want to mount it away from other wires or anything flammable as it will get hot. Normally you mount it on the firewall above the engine. Just cut the wire, add connectors and hook one wire to one prong of the ballast resistor and one to the other.

Here's some ballast resistor parts numbers for you:

-AC Delco part # C1101
This is a single ballast resistor with a mounting bracket.

-Napa part # ICR-13 (Echlin)
This is also a good firewall mounted ballast resistor.

How about the points?

The 6v points will be just fine and are usually just a little tougher than the 12v points.

Now for the condensor.

You need to change it. Any late model condensor will work. All you really have to worry about are the mounting and the ends.

Here are some condensor part numbers for you:

-AC Delco part # A202Z
This is open lug with side mounting bracket.

-AC Delco part # E211
This is a closed lug with a rear mounting bracket.

-AC Delco part # F204Z
This is open lug with a rear mounting bracket.

Tip: If you have any trouble at the parts store on these ignition parts or they want a car, just go with late sixties - early seventies Chrysler products. They work very well.


Let's make those guages work.

First, all the bulbs in the guages and guage clusters as well as any other bulbs in the dash or interior need to be changed over to 12v. Just take the old ones in and match them up to 12v bulbs.

If your guages are mechanical, they're fine. If they are electrical, they need a ballast resistor to make them work. If you have idiot lights, you just change the bulbs.

The amp guage will be fine. However, if going from positive ground to negative ground you just need to switch the wires side to side or it will read backwards.

Some fuel guages work just fine on 12v while others don't. You won't blow it up, but if it doesn't read right after switching over to 12v, it probably will need to be run through a ballast resistor. Just put it in the power feed to the gauge.

The rest of the guages will need a ballast resistor of some kind wired into the power input of the guages.

Heres some possible part numbers for ballast resistors for your guages. Look them up and see what will work best for your needs:

-AC Delco part # U1745
This is what it says: "Voltage reducer. Reduces 12 volts to 6 volts. 1.5 ohm resistance for 4 amp maximum load. Permits use of regular 6 volt accessories on 12 volt systems. Mounts through 7/16" diameter hole. Includes clamp on bracket."

-AC Delco part # F610 and F611

-Napa part # VT6187 (Echlin)
This may be the best option. One unit can feed all your seperate guages. Just run a wire from the ignition switch to the unit and another wire from the other side of the unit to one guage then jump wire to the next guage and so on.

Remember to mount these ballast resistors where they won't melt any wires or catch anything on fire as they will get warm or hot.

If you don't want to mess with the original guages, have a rats nest of bad wiring under the dash, or after a quick and easy way to wire up guages the aftermarket is the way to go. Just go with aftermarket guages and sending units. It's often easier and you know they will work.

Don't forget the radio. About the only way to convert your radio is take it to an automotive radio repair shop. If you can find one. Probably the best bet is to find one on the internet and send it out. However, it's probably gonna cost ya. Ballast resistors really don't work on radios as they are very specific about power. Replacing with a new system is usually the cheapest.

However, if you want to retain the looks of your radio, a lot of people leave it in and hide a newer radio somewhere within reach. Or, look in hotrod or streetrod magazines as there are aftermarket options that mimic the look of your old radio or actually work through your existing radio.

Blower Motors and Wiper Motors

These 6v electric motors won't last long on 12v. They can be made to work usually with a heavy load ballast resistor. However, it may be easier and sometimes less expensive to just change the motors out for 12v ones.

If you want to use heavy load ballast resistors try this part number:

-Napa part # VT6187 (Echlin)

Now then, on to the lights.

Lighting System

This usually is fairly simple.

You DO NOT need to switch your headlight switch, the brake light switch, headlight high beam switch, the headlight circuit fuse and the turn signal fuse. They are just fine for a 12v system.

You will want to change your turn signal flasher for a 12v unit. Just take the old 6v one in and match up a 12v replacement. The wires connect to the similarly labeled terminals on the 12 volt flasher.

Now just change out the bulbs. Look closely at the sockets and make sure they are clean and not corroded. Usually you can just take one of each type of 6v bulb you have and find its 12v equivalent. You want to pay attention how the base is made and the size of the bulb. Sometimes you may have to change out the pigtails in a socket to make them work. Pigtails are the bottom terminals that push into a socket and have the wire ends. Or you may just change the entire socket.

Ok, now that's done...

Now for some final things you might need to look at...

Do you have any relays? Some older vehicles have them and you need to change them to 12v versions. Look through your wiring. Things like horns might have them. You may not have any at all.

Look at your ground straps!

Almost all electrical problems can be traced to bad grounds. Some really weird and seemingly unrelated stuff can happen if you have bad grounds.

You can never have enough ground straps. Especially if you start adding accessories. You should have a cable from the negative post on the battery to the engine block, a strap from the engine to the firewall, a strap from the dash to the body isn't a bad idea, a strap from the body to the frame or the battery negative post, and a strap from the frame to the engine block. It sounds like a lot, but if you start looking through your car, you probably have most of them already. Make sure your grounds have clean connections and aren't in bad shape. If you're unsure, just put on another one. It's cheap insurance.

And finally...

When you do your electrical work, be neat. It makes things so much easier to work on in the future and looks professional. Remember, you're building skills here... Take pride in your work. Use good materials, stick to the same wire colors, bundle your wires up into looms, fasten wires up neatly out of the way, etc.

Also, this isn't the final work on how to do a conversion. Every car is different and you should look up information for your particular model. A good thing to do is find a forum on the internet that deals with your particular car. There you can find lots of specific information on your kind of model and maybe even stuff you never even thought of. A little homework can save a lot of fustration.

Good luck!

Return from 6v to 12v to Hotrod Wiring

Return from 6v to 12v to How-To-Build-Hotrods

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