Convert 6 Volt Car to 12 Volts
In 1955, 12-volt electrical systems became an automotive industry standard. The reasons for this change were two-fold. First, car manufacturers were producing new, higher compression V8 engines that needed more starting power. Second, new features such as power seats, power windows, etc, were putting more of a demand on electrical systems.
Before converting your 6 volt car to 12 volts, ask yourself a couple questions:
How often do you drive the car?
Is the motor stock or does it have performance mods?
Are you adding power accessories, such as halogen headlights or LED taillights, or an aftermarket radio and amplifier?
12 Volt Benefits
Engines built prior to the mid-fifties should not have any problems starting with the original 6-volt system. This is providing the battery and electrical system are in good shape and that the motor has not been extensively modified. If you have trouble starting the car when the engine is hot, a 12-volt system will provide more cranking power.
Other benefits of converting from 6 volts to 12 volts are improved headlights, as well as the ability to add 12v accessories. Keep in mind, if your 6 volt system was not working correctly to begin with, the difference will seem more dramatic.
A 6-volt wiring system and switches are more than enough to handle 12 volts. This is because it's heavier because 6 volts has to carry more amperage than 12 volts. Less volts means more amperage. Changing to 12 volts cuts the amperage load approximately in half. However, that 50-year old wiring is usually cracked and frayed and would need replacing anyway. But if it's in good shape, there's nothing wrong with using 6 volt wiring in a 12 volt system.
Make sure the new battery will fit! You may also need new cables to accommodate the different size battery. Don't forget to reverse the cables if your car was originally a positive-ground system.
Some classic car owners have replaced their 6-volt battery with an 8-volt battery. This will give more starting power and will not hurt anything in the electrical system, but may shorten light bulb life. When an 8 volt battery is used, the voltage output needs to be raised. Many old cars have voltage regulators that are adjustable. A small adjustment to 8.9v to 9.4v should keep an 8-volt battery charged up.
Generator vs Alternator
If you have decided to change your 6 volt car to 12 volts, but want to keep things looking original, you can have your 6-volt generator converted to 12-volts. This is done by replacing the field coils with 12-volt coils. A note of warning - there aren't many electrical shops that do this on an everyday basis. Look for a place that services the old car hobby. And don't forget to replace the voltage regulator with a 12v unit.
read Old Car Electrical Systems
Advantages of an Alternator
If you are planning to add power accessories, such as a radio, electric cooling fan, power windows or power seats, halogen headlights, etc, you must use an alternator, as generators cannot keep up with the amperage required. Switching from a generator to an alternator has one major drawback, though - you lose originality. You'll have a big, unsightly alternator sticking out like a sore thumb.
Many old car enthusiasts who switch from generator to alternator use the one-wire GM type unit, the 10SI model. These units are small and inexpensive, and easy to wire in. They also do away with the stock voltage regulator as they have an internal regulator built-in.
Several aftermarket companies, like PowerMaster Performance, offer an alternator that looks like a generator. You get the traditional look of a generator, but it's actually a 12-volt, negative-ground alternator that produces 65 amps at idle and 90 amps going down the road.
The PowerMaster alternator is really the best of both worlds. You get the performance of an alternator but keep the looks of the original generator.
Shop: PowerMaster Alternator
Automotive starters are heavy-duty electric motors designed for short, intermittent bursts of voltage. After installing a new 12 volt battery and 12 volt solenoid, the old 6-volt starter can still be used. This may shorten the starter's life, but if your engine starts quickly, a 6-volt starter can last a long time in a 12-volt system. On the other hand, if your engine has to be cranked for long periods before it starts, change the starter to 12 volt unit.
Light Bulbs And Switches
Headlight, tail-light, parking lights, dash lights, dome lights, etc., all bulbs must be replaced with 12 volt bulbs. You can use your headlight switch, brake-light switch, and high-beam switch. They will work in either a 6v or 12v system.
6v to 12v Gauges
If your gauges are mechanical, there's no problem. If they are electrical, they will need a voltage reducer to make them work. If you have warning lights on your dash, the bulbs must be changed.
Even after 12-volt systems were introduced, Ford retained their 6-volt gauges for many years, right up into the seventies. Instead of manufacturing new gauges, Ford designed a voltage-drop regulator, also known as a voltage reducer. These are easily obtainable, as they were used on many years of Ford cars and trucks.
Blower Motors and Wiper Motors
Aside from starter motors which are used in short spurts, electric motors designed to run on 6 volts won't last long on 12 volts. A voltage reducer would help, but it's better to replace the 6v motors for 12v ones.
If you have turn signals on your vehicle, the 6-volt flasher must be changed to a 12-volt type. This will allow the signals to "blink" correctly.
Although some will, most 6-volt horns will not work on a 12-volt system. Replacement 12-volt horns are plentiful and cheap.
Distributor and Ignition
The ignition points themselves will work with either 6v or 12v, but the points condenser should be changed. Buy a 12 volt ignition coil. They have more windings and work much longer.
Read: Points vs Electronic Ignition
Some 12v coils need a ballast resistor and some don't. If the coil that you're using requires one, install it between the ignition switch and the coil. Be sure to mount it away from other wires or anything flammable as it gets hot. They are usually mounted on the firewall above the engine.