6->12 Volt Conversion
Originally posted to the Vanagon list on 07 Oct 1995
I've noticed a few questions about 6 to 12 volt conversions recently.
Here's my experience, plus some stuff from a 1989 VW Trends article.
Let me repeat: these are *my* experiences. Yours may differ. See
The wiring harness should not require replacement. However, this
would be a good time to check for breaks in the insulation, or in
the wire where connectors attach. Any problems along those lines
should be addressed, particularly semi-broken wire. Cleaning
up any corrosion would be a good idea, too.
The flywheel on stock 12 volt engines is larger than on stock 6 volt
engines. My experience has been that keeping the 6 volt flywheel
(and corresponding `bendix' on the starter solenoid) works fine. As
a corollary, using the 6 volt starter works very well in a 12 volt
system. This is because you aren't running the starter motor for
very long, so the higher voltage doesn't cause it much of a problem.
It also causes the thing to spin faster, which makes for easier
Remember to replace everything that even vaguely resembles a light-
emitting device (head lights, tail lights, running lights, ...). In
particular, don't forget the oil pressure warning light. Thanks to
opposite advice from someone that should know better, I toasted an
engine by not doing this -- it promptly burned out, the engine had a
leak, and you know how it goes from there.
You'll need a new generator. The VW Trends article suggests the
Bosch GR26X. It has the advantage of being the same size as your
existing generator, so you can use the generator stand, pully, and
belts that you've already got. I went with a slightly larger one,
that required swapping out all the other stuff, also. I had
significant problems finding belts that fit.
If you have an electric choke, you'll need to get a 12 volt version.
They're the same size on Solex carbs, so if that's what you have,
you're in luck. Since you have a 6 volt system, you probably have a
Solex carb. I can't imagine anyone having upgraded the carburetion
without having changed the electrical system also (but then, I'm
often accused of not having sufficient imagination).
You've got a couple of choices for handling the 6 volt motor things
(primarily the windshield wipers, but also the heater assist fan if
you've got one). Choice A is to put in a voltage-dropping resistor.
This solution is quick and easy, but not a good one in my
experience. First of all, you end up throwing away quite a bit of
electrical power in the form of heat in the resistor. Secondly,
using a resistor as a voltage drop only works if you know how much
current you are going to be pulling (voltage = resistance *
current). So, you either have to measure the existing resistances
and do some math, or hope that the off-the-shelf unit you get is
close enough. And you are still left with the painfully-slow 6 volt
wipers. Choice B is to replace the motors with their 12 volt
equivalents. This is certainly more work, because you have to
physically remove the existing motor(s), find replacements that will
fit (both into the mounting brackets, and into the shaft
attachments). I went the first route, and am planning on ripping it
out and doing it right.
I'm not real sure about the fuel gauge. I don't have that
particular vehicle any more, so I can't really say much on the
topic. I seem to remember it failed a few months after the
conversion, though, so I suspect that it might need to be replaced.
Although not really required, this would be a good opportunity to
replace the plugs, wires, points, and condensor. There's no
difference between the 6 and 12 volt versions of these (i.e., there
are no separate versions), but these components are subject to
extreme conditions, and replacing them just eliminates one more
Here's stuff directly cribbed from the VW Trends article:
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Parts list: headlights, coil, turnsignal/emergency flasher unit,
all the other light bulbs, battery, voltage regulator.
The 6 volt horn will last a while, but will eventually burn out.
Depending on what year you have, swapping the entire wiper gear and
motor assembly out may cause your wipers to stop in the opposite
position than they used to. There are replacement switches and such
available to fix this. This problem is why I suggested just
replacing the motor above.
Lots of places have conversion kits. Call up and ask.