Install a 6 Volt Alternator on Your Old Car!




About: I work as a chemical operator. In my off time I enjoy spending time with my family and working on my "old" Fiats and my latest edition, my '81 Trabant 601.


So you have an old car that has a 6 volt electrical system and you want more electrical power. Most people will just swap out the generator for a typical 12 volt AC Delco 10-SI alternator. The problem with doing this is, you have to change just about every component (or install drop down resistors), and bulbs. This is OK if you have a donor car or access to all the parts but if not what is a cheaper, easier, yet just as effective alternative? Go with a 6 volt alternator!

Voltage and amps explained:

The only thing you do not have to do when going to 12 volts is replace the wiring since doubling the voltage will drop the amps in half. The thickness of the wire has to do with amps, not voltage.

I think 6 volt automotive systems get a bad wrap. Dim lights, slow wipers, etc. It's not the voltage but the fact most generators produce low amps (~30 amps) and don't charge well (if all) at idle or low engine speeds. Also 6V electrical systems haven't been used in years so by now, there is lots of resistance in the system due to corroded connectors anyway.

Think about it. The United States uses 110V AC at 60 HZ where other countries use 220V at 50 HZ. Are their electrical systems really any better than what we use? Just because they double their voltage?

The only bad thing I can really say about 6 volt electrical systems is bulbs are typically more expensive and the lack of modern components available for 6 volt systems like radios.

But because the voltage is doubled, the amps drop in half. So you can get by with using smaller wiring. I suppose at some point automakers figured if they doubled the voltage they could use less copper and save money. Who knows maybe one of these days 24 volts will eventually become the new standard in automotive electrical systems if the price of copper goes out the roof.

Not saying 6V electrical systems are better than 12V systems, but if someone can explain why 12 volts became the standard other than getting by with smaller wiring, then I'd like to hear it.

In my case, I had added several components to my 1981 Trabant 601. The last car in production on the planet still using a 6 volt electrical system until IFA went to a 12 volt alternator in 1984. Some components I've added go through a 6 to 12 volt converter such as my radio, fuel guage, electronic ignition, LED backup light licence plate frame. It wasn't until I added a 12V electronic ignition did my generator light start to glow at times because it pulls more amps than the other 12 volt components combined.

I also upgraded from the standard 40/45 watt R2 incandescent headlamp bulbs to brighter 50/55 wattt H4s and 55 watt auxillary lamps which come on with the high beams. So just the high beams and auxillary lamps alone almost exceed the 220 watt generator/regulator's capacity. It was clear I needed more electrical power!

Step 1: The Alternator and Bracket

The alternator:

This is a typical AC Delco SI-10 model. The same alternator used on just about everything GM back in the 1970s until the early 1980s. Except it features a 6 volt internal regulator and produces 60 amps, twice what my Trabant's generator produced. You can get these in "one wire" models but I chose the older "3 wire" regulator. My main reason was my car is air cooled and has no temperature guage. So I needed some way to alert me if the V-belt broke. Plus the "one wire" versions I've read don't react the voltage drops and there is no way to get a charge indicator lamp to work. This link below explains it:

The bracket:

The alternator included an adjustable bracket that bolts to the generator bracket in order to align the pullies. I just so happened to have a spare engine laying around which made it easier to check for clearances.

The alternator and bracket cost $145 plus $25 for an upper bracket and V-belt. This was far cheaper than replacing everything on the car even if I used an old 12V Bosch alternator I had laying around. Shipping alone heavy parts from Germany to the United States is not cheap!

I bought this setup off Ebay. They are typically sold as one wire alternators but I asked the seller if he could supply me one with the old style regulator so I could use my charge indicator lamp.

Step 2: Test Fitting

Once I found a suitable angle for the alternator which cleared the carburetor, I adjusted the bracket and checked the alignment of the pullies with a piece of threaded rod. I used this same method when I built an air conditioning system for my Fiat Spider.

The rod appears to be at an angle but that is an optical illusion because the motor is not sitting level on my garage floor.

Step 3: Belt Tensioner Bracket

The kit did not come with a belt tensioner bracket. Sometimes you can use the generator bracket if it's long enough and space it out with flat washers or just make your own. In my case the generator bracket was too short.

So I purchased this chrome dressup bracket available at just about any autopart store for $15. I had to remove about half of it then drill a new hole at the end and reshape the end on a bench grinder. I traced out the bracket on a piece of cardboard to use as a templant before cutting.

A good way of finding the center for the hole is to measure the width which was 1". Then measure the length from the end and make a 1" mark then another mark at 1" on the other side and then draw an X between the edges to the marks using a straight edge then drill a hole where the two lines cross.

Spacing the tensioner bracket at the engine:

Tighten the nut that secures the bracket to the alternator. Then add flat washers between the engine block and bracket to make up any difference so it's aligned.

Step 4: The V-belt

I needed a longer V-belt. The method I used was to center the alternator in the middle of the "curve". That way if the belt was a bit too long or too short I could go in either direction.

I wrapped an electrical cord around all three pullies then overlapped them at a point and made two reference marks where both ends overlapped. I suppose you could use a string if you want to. Then took it to the autoparts store and had them wrap it around their belt measuing tool.

Unfortunatly they did not have any belts 1" shorter than this one! The next size down would have been too short.

Step 5: The Wiring

This was actual not as bad as I expected. With this step you may need to find a wiring diagram for your car. But the wiring going to and from the old generator and external regulator are probably not much different than my car.

First the alternator. There are three wires involved. One is a thick wire (8 AWG) that runs from the post on the alternator to the post on the starter. This wire will overlap a thicker wire which goes to the POS post on the battery.

On the GM regulator, there is a connector with two smaller wires, a white (maybe yellow) and a red wire. The white wire is the field wire. The red wire is the sensing wire.

The white (or yellow) wire get's it's power from the ignition switch (when on) through an indicator light in series.

If the alternator produces no power, it grounds the bulb and lights it up. If you chose not to use a bulb as an indicator, then substitute a resistor. I don't know what size because in my case I wanted an indicator lamp. Don't run this wire directly from the ignition switch to the field wire on the alternator!

The red wire is the sensing wire. This wire is connected downstream to compensate for an voltage drops say to the fusebox or some other junction point and is powered at all times. You can connect it directly to the post on the alternator but this is not ideal. See the link I posted above.

Generator/external regulator:

At the regulator there were five wires. Three of which went to the generator. An input, output and a ground. Once the generator and it's wiring harness were removed, this left me with two wires. A thick red wire and a small blue wire.

The thick red wire went to the starter post, ignition switch and fusebox. The small blue wire powered the external regulator and also served as the charge indicator. Luckily the indicator lamp on my car was wired in series just like on a GM vehicle.

I chose to run a new 8 AWG wire directly from the alternator to the starter. I connected the red sensing wire to the old power wire which is downstream to compensate for any voltage drops. Then the blue wire connects to the field wire (yellow or white).

If you are not sure which wire powered the old regulator, pull the indicator lamp socket out of the dash (if there is one). Make sure it's wired in series and it's color and trace it down to the regulator. Disconect it from the regulator and start the engine. The light should be out. Now touch this wire to ground and see if it lights up. If so then connect it back to the regulator and if the light goes out, if so then your good to go!

The regulated output wire from the regulator will most likely be a thick wire and have power on it at all times.

If your regulator has more than 2 wires once the generator and the wires that go to it are removed, you'll need to get a wiring diagram for your car or trace these wires down to see where they go. They may just be additional regulated output wires which goto the fusebox and can be tied together. Two of which may go to an ammeter guage. Or an additional ground wire.

Make sense so far?

Step 6: Final Testing

As when working on an electrical system, it's a must that the negative post be disconnected. Before reconnecting the negative post, tap it slightly and check for any excessive sparking. This will indicate something is not wired up correctly. You will know if something is not correct in a hurry (smoke)! It's best to use a 60 amp fuse between the alternator and starter when in doubt.

Now start the car and using a voltage meter check for voltage directly at the battery. You may have to rev the engine up a bit at first but it should produce around 7.3 volts at idle.

Initially it seemed when I turned the headlamps on, the idle speed would drop significantly. But after I replaced the battery cables, the problem went away.

The results:

Headlamps and dashlights are brighter, don't dim at idle, wipers are faster, turn signals flash quicker, charging light never glows. Even my accessories after my 12 V converter work better.

Step 7: Fusebox Upgrade

One more thing worth mentioning. My car came with the typical European style fusebox. As you can see due to the resistance this caused all sorts of issues. Particulary melted insulation from hot headlamp wires. No amount of cleaning seemed to help. Rather than replacing it with the same type, I decided to install an ATO type. This works much better and no more heat! ATO fuses are far superior to the old type. ATO fuses will actually blow if you feed too much current through them. The older type fuses will only blow if short circuited. They typically just get hot and melt.

Let's not forget to clean and replace other corroded or rusted connectors which accounts for alot of resistance which causes voltage drops.

Good luck!



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    5 Discussions


    7 months ago

    Good instructable.

    One question though. I know this is 3 years old, but is the eBay seller that you got your alternator through still doing business? If so, could you post his name? The reason I ask is that I am having an impossible time finding a 3 wire alternative to the 1 wire setup. Or if you know the part number to your alternator or voltage regulator, that would be handy to know too.

    As you pointed out, there are advantages to the 3 wire system that I would like to enjoy.



    4 years ago

    I need to read through some old books I'm sure it's possible to make a 12v alternator run at 6v
    my recollection is it required the removal or by passing of the 12v regulator and fitting a 6v external regulator

    1 reply

    Reply 2 years ago

    Get an externally-regulated alternator to skip the step of having to take it apart and bypass the internal regulator. Then either build or buy a regulator for 6v. They cost about $100.

    These days you can also get an internally regulated 6v alternator in positive or negative ground.


    2 years ago

    The higher voltage became the standard because it makes the electrical devices running on the system more efficient. Amps are what requires the bigger wires, amps are also what turns into heat. 12v starter motors turn harder for their size and weight and require less cooling. 12v lights are brighter without the fixture having to be as heavy. The only reason anybody ever bothered with 6v systems was because that's what they could get out of a generator. Once diodes were invented alternators generate power much more efficiently, are cheaper to build, and require practically no maintenance. And because of their simpler construction and better efficiency they can produce much higher voltages. Before power inverters got cheap there were boxes you could hook to the externally-regulated alternator on your vehicle to kick it up to 120v so you could run your appliances off of it. 12v is a good tradeoff for a car electrical system between cranking and lighting power and the number of cells you have to stuff into the battery compartment.

    Yay more car DIYs! I will full on admit that cars are a complete mystery to me, but I still managed to follower your instructable. Very nice job explaining your process!