Converting from 6 Volt to 12 Volt
by Chris Pratt
You get up on your old tractor and hit the starter button and out comes rrunh... rrrunh.... rrrruhn..... rrr..click.
It's a common problem for old machines especially when the weather starts to dip below 40 and the tractor isn't
fired up as often. You are probably used to the 12 volt Diehard, charged with 200 amp alternator of your 3/4 ton
that always is ready and always starts. It's this type of experience that brings about the many queries we get
for 12-volt conversion kits. Since only a few kits are available (we sell kits for the Ford
9N/2N/8N and the Ford NAA and other tractors), this article will explain the basics of the conversion
and what you can do if no kit exists for your tractor. Before we do that, lets see what the alternatives are to
avoid converting and for those machines that really should not be converted.
To Convert or not to Convert?
If your tractor is a working tractor, there is little reason not to convert beyond the cost. A 12 volt system
is a bolt-on cure that masks the many ailments of hard starting machines without the time and expense of teardown
and rebuild. The original 6-volt system will suffice if the tractor is well maintained with optimum tuning, good
compression, correct gas flow, and minimal losses in the wiring. In the real world, it is difficult to invest the
time necessary to keep up on all these issues and 12-volt conversion becomes inviting. Still, the most compelling
reason to convert to 12-volt is that your existing 6-volt system has serious problems and requires replacement
anyway. When this occurs, it may actually be easier and less expensive to convert. Locating original components
may be very difficult and time-consuming.
On the other hand, if your tractor is rare or you're are restoring it for originality or show, it would be a
cardinal sin to update the electrics to 1990's standards. In this case, you will have to take the time and expense
to make the 6-volt system work as it was intended. Normally this is not a problem because the your restoration
process will need to cover all the issues that make the original system work well anyway.
What do I replace (or what do I reuse)?
If it seems that conversion is the right thing for you, several things will need replacement. Due to some oddball
items used on a few machines, it is hard to be definitive on this but for the most part the following list shows
the items that will have to go on most tractors:
- Generator - Since the generator is not made to produce 12-volts, it cannot be modified to charge a 12-volt
battery. Remember to save your old generator, someday you may want to restore your tractor or if you sell it, someone
else may want to. When you look for your new replacement alternator, be sure to match the pulleys as closely as
you can. The issues are the width of the belt, depth of the belt (determined by its v-shaped profile), and the
diameter of the pulley.
- Light Bulbs or Light Assemblies - 6-volt lights will instantly burn out. If you have the original lights, you
may want to consider picking up inexpensive 12-volt light replacement assemblies. It may be difficult to find bulb
replacements that fit in the original assemblies and it will pay off later to keep the original components in original
condition. There are a range of available light assemblies that go from large steel case models to very cheap rubber
- Regulator - The regulator is made to cut the circuit to the battery and regulate the output of the generator...
of a 6-volt system. It will not work with your new system and in any case, many replacement alternators will have
the regulation built right in. If not built in, you will still have a new 12-volt regulator that matches your new
- Battery - Here is where you get to go buy that new Die-hard. You will have to match the size and shape of the
existing battery to avoid changes to your battery box. Since you will have to exchange your old battery, take it
in and accurately compare the profiles; height, width, and length.
- Generator Mounts - It's almost impossible to find an alternator that matches your existing generator mounts.
The good news is that making new mounts will frequently mean simply getting some bar stock from the hardware store
and spending a bit of quality time with your hand drill and file. Usually you will have to use spacers or washers
on the pivot point to line the new alternator up with the other pullies. Once you have this roughed in, you will
drill a hole in your bar stock to attach the mount to the engine and then drill several closely spaced holes to
provide the adjustment slot. To finish the mount, you will have to file out the material between the holes leaving
a slot that allows the adjustment of the belt. There is the possibility that one some tractors this mount will
need an angle. In this case, you will have to cut everything out and take it to your local welder for completion
(don't be afraid of this step, the welding still won't cost more than 10 dollars).
- Fuses - Since your fuses are rated for a 6-volt system's amperage, they will likely not blow when they should.
They should be replaced with lower rated fuses. To determine the correct rating, you must determine the draw of
Now the best part, what do you get to keep. The following items can be reused, but be sure to understand the
- Coil - For battery ignitions, the component that is 6 or 12-volt specific is the coil. You could put a 12-volt
coil on the machine or use a ballast resistor on your existing 6-volt coil. During the 6 to 12 volt transition
period in the late 50s and early 60s, it was common for new cars to be equipped with 12 volt systems employing
a 6 volt coil and ballast resistor. For Magneto ignitions, there is no change since the magneto is a completely
separate self-contained electrical system is not impacted by the 6 or 12-volt system.
- Starter - The existing 6-volt starter not only can be reused but most often is your only option. It is improbable
that you will be able to locate a 12-volt starter that will match your drive gears and mounts. Still, real caution
must be used to avoid burning out your starter. The starter will get hot under 12-volt use so you should avoid
cranking for long periods and let it rest between attempts. Keep your tractor tuned up and this should not be a
- Wiring - If your wiring is in good shape there is no reason to replace it. The 12-volt system will draw 1/2
the amperage so your heavy gage 6-volt wiring will more than match the need. If your wiring is in questionable
condition, the conversion is a great excuse to clean it up and eliminate any future problems before they start.
It may be a good idea to wire for a 6-volt system in case you do restore in the future.
- Ammeter - Your ammeter will work fine but will show discharge when your system is charging and a charge when
your system is discharging. This is because you will be reversing the polarity of the battery from positive ground
to negative ground to match your new alternator. This is easily fixed by reversing the leads on the Ammeter.
In summary, here is a possible scenario for doing this job.
- Locate your lights, fuses, battery and alternator. If you can't find a good fitting alternator with internal
regulation, you will also need a matching regulator.
- Build your mounts
- Rewire any poor circuits
- Install the Alternator (and regulator) according to manufacturer provided wiring instructions
- Install new lights and fuse
- Reverse the leads on the Ammeter
- Install the Battery with the negative pole grounded
- Install a ballast resistor on the coil if you have a battery ignition
Here is an article giving the step-by-step conversion for many tractors using the one-wire alternators we carry..
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