Converting a 6 volt Positive Ground 1930 Model A Deluxe

By Stuart Vogel

First let me point out that my ultimate goal is to air condition my sedan using a system designed and built by Kenneth Davis who constructs these systems at his shop in Colleyville, Texas since the air conditioning system will not work on a 6 volt electrical system.

I want to thank Fhane Jones for his assistance in supplying the components that were needed in order to make the conversion a success and Harold Fienberg for his invaluable technical assistance.

The items that you will need are as follows:

1. 12 volt battery (I chose a maintenance-free battery)

2. 12 volt tail/stop lights (I chose the LED inserts so I did not have to replace the housings)

3. Horn resistor so I would not have to replace the existing 6 volt horn

4. 12 volt ignition coil

5. 12 volt alternator

6. 12 volt electric wiper motor (if your car is equipped with a 6 volt motor).

7. 2 amp in-line fuse for the wiper motor if there is not one already being used.

8. 12 Volt light bulbs:

Two headlight bulbs

Two cowl light bulbs (if your car is equipped with cowl lights)

One dash light bulb

One dome light bulb (if your car is equipped with an interior dome light

Tail/Stop lights (see item # 2 above)

9. 30 Amp ammeter (if your car is not already equipped with one)

10. 12 volt starter motor (Remove the Bendix and Woodruff Key from the old starter for use on the 12 volt starter motor)

11. A battery cutoff switch (if you do not have one already installed)

12. Polarity tester device to test 12 volt coil wires

Now for the conversion work:

1. Disconnect and swap out the 6 volt battery for the 12 volt one but make sure that you do NOT connect the battery at this time.

2. Install a battery cutoff switch if your car does not already have one.

3. Install the horn resistor as per the simple instructions. The resistor is connected between the yellow horn wire and the wiring block inside the horn cover and allows a 6 volt horn to be powered by a 12 volt system without damaging the horn.

4. Install the 30 amp ammeter and make sure to reverse the wires on the back of the ammeter since you will now be using a negative ground for the electrical system.

5. Replace all light bulbs with the 12 volt bulbs.

6. Replace the existing 6 volt ignition coil with the 12 volt coil. Do not reverse the wires; keep them on the same side as they were when using a 6 volt coil.

7. Replace the 6 volt generator with a 12 volt alternator and connect both wires from the generator to the lug nut on the back of the alternator.

8. Install the Bendix drive onto the 12 volt starter using the Woodruff Key and making sure to use new lock washers with the bolts holding the Bendix to the motor shaft.

9. If you had an electric wiper motor replace the 6 volt motor with the 12 volt motor with a 2 amp in-line fuse if there is not one already there.

10. Connect the battery cables to the 12 volt battery making sure that the positive and negative cables are connected to their appropriate battery posts.

11. Turn on the battery disconnect switch and test the lights, horn, etc to make sure that the system is functioning properly. Check to make sure that the ammeter registers in the discharge side of the meter when the lights are turned on. If not you probably forgot to reverse the wires on the back of the ammeter. If all is in working order then you should have no problem in starting the car.

12. Turn the battery disconnect switch to the “OFF” position and unplug the ignition coil wire from the top of the distributor cap and plug it into the top of the polarity tester. Plug the bottom of the polarity tester into the top of the distributor cap.

13. Turn the battery disconnect switch to the ON position and start the motor and observe to see that the upper light on the polarity tester is illuminated. If it is then the polarity of the coil wires is correct. If the bottom light on the polarity tester is illuminated then the wires on the ignition coil need to be switched. If the wires need to be switched turn off the motor and turn the battery disconnect switch to the OFF position. Switch the wires at the bottom of the ignition coil. Turn the battery disconnect switch to the ON position and start the motor. If the top light on the polarity tester is illuminated then the coil wires are properly connected. Turn off the motor and switch the battery disconnect switch to the OFF position. Remove the polarity tester from the top of the distributor cap and re-insert the ignition wire into the top of the distributor cap. Make sure that the ignition wire is tightly plugged into both the distributor and ignition coil.

Turn battery disconnect back on and start the motor. It should start OK and you’re good to go!