Tim Dapper shows you how to do the conversion to 12 volt.

Here are the steps to change your Type 34 from 6 volts to 12 volts:

  • Change the cast aluminum fan housing, and install the larger 12v generator. It is possible to get a 12v generator the same size as a 6v, so that you do not have to change the fan housing. Try Bill & Steves.
  • Change the coil.
  • Change the chokes.
  • Change the idle cut-off solenoids.
  • Change the flywheel. Use an automatic transmission starter so that you do not have to change the starter shaft bushing. There was a flywheel hub design change, as the older crank shaft end had a bulge. The flywheel has a step cut into it to clear this bulge. It is probably easier to have a step machined into the flywheel hub than to disassemble the engine to have the crank shaft end dressed. Finding the correct flywheel is best. Finding the old style hub flywheel with a removable ring gear (and the correct ring gear to go on it) is next best, but harder. A 6v bendix gear in a 12v starter is rare, but I suppose that you could disassemble a 6v starter, and have the gear welded and redrilled for mounting in a 12v starter. Or don't change the flywheel and put a 12 volt solenoid on your 6 volt starter. Or don't touch anything and run your 6v starter until it burns up.
  • Change the voltage regulator.
  • Change the battery. Your battery cover will not fit anymore.
  • Change the windshield wiper motor. Or install a resistor to cut the voltage. Or run your wipers really fast until you burn them up.
  • Change your wiper switch to a 12 volt switch. There are reports of 12 volts overstressing and burning out 6 volt wiper switches.
  • Change the fuel gage in the dash. No need to change the sender in the tank.
  • Change the clock. Or don't worry about it because it won't run for ever anyway.
  • Do something with the radio.
  • Change the headlight relay.
  • Change the turn signal relay.
  • If you have a horn relay, change that. Change the horns.
  • Change every light bulb, everywhere.

That ought to about do it.

Does anybody get the idea that a 6v to 12v conversion is quite a bit of work, not all of it simple?

The easiest thing to do if your 6v electrical system is getting tired, is to put a 6v horn relay (from a Karmann Ghia) in the solenoid circuit, so that your solenoid can get a full 6 volts. You can do a similar trick in the coil circuit. If you think your wiring is getting tired, try measuring the voltage at the coil. When internal resistance drops the voltage to less than about 5.5 volts, you will have trouble starting the car from weak spark. A similar test at the solenoid will tell you that you will have trouble getting the starter to work consistently. You can also replace the stock battery cable, which is about 4 gage (I think), with a heavier gage cable to be certain that there is no voltage loss going to the starter. If you change the positive battery cable, you might also want to secure the starter ground, by putting a longer bolt through the body where the battery is grounded now. Under the car, run a cable from the longer bolt to one of the starter mounting bolts. This gives you a more direct ground, again to avoid voltage drop at the starter. This 6v clean up stuff is a lot easier than a 12v conversion, and lets you keep your car stock because no body can see your modifications. Of course, a 12 volt system is not so subject to tired harness disease, and lets you use a modern radio.