Upgrading Your Classic Car from 6V to 12V: What You Need to Know

So, you’re looking for convert your Flathead Powered Ford over to 12V?
If you own a classic car from the 1930s to the mid-1950s, you’re likely familiar with its 6-volt electrical system. While these systems are durable and can last for decades with proper maintenance, many enthusiasts opt to convert to a 12-volt system for better compatibility with modern electrical components. Here’s a comprehensive guide to help you through the conversion process.

Retaining Existing Components in Your 6V to 12V Conversion

Converting your vehicle from a 6-volt to a 12-volt system doesn’t mean you’ll need to replace every component. Key parts such as your starter, distributor, and gauges can often be retained. If your electrical wiring is still in good condition, you can also keep that in place. Just inspect the wiring and make sure the fabric coating is not warn or the inner wiring exposed. 6V wiring is quite a large gauge wire. Although it is less voltage it is greater amps. Which requires a fatter wire than 12V. So, your new 12V system will work perfectly with your old wires.

Essential Upgrades:

• Voltage Regulator: The voltage regulator must be upgraded to 12V versions.
  
• Ignition Coil: Replace the 6V ignition coil with a 12V coil. Remember that coils are directional. So don’t mount a coil sideways if it was designed to be vertical. Also to make sure you don’t have problems, do everything you can to mount it in a place that isn’t going to be too hot. Mounting the coil with a metal bracket to say the head can cause the coil to show symptoms like vapor lock. Or boil the coil all together.
  
• Ignition Ballast Resistor: Install a 12V ignition ballast resistor specific to your vehicle’s make (e.g., don’t use a GM ballast resistor on a Ford vehicle).
• Starter Relay: Install a 12V starter relay to insure no problem when starting the engine.
• Battery: It should be said that one of the most common batteries used on this conversion for those that can is a Gel Cell Optima red top battery. I say this with the upmost sadness. These batteries are not what they use to be in the late 90s-early 2000’s. They are of a much lower quality and shorter live span. My truck has an optima from 2002-2015. With no problems. I swapped it out when it died and it lasted 4 years under the same conditions. I have since swapped to a yellow top Walmart battery and the battery is still going strong after 6 years and has better cold cranking amps in cold weather than the second optima did. Save your money.

For reliable parts, consider sourcing your condenser from Napa. They are known for offering dependable components with fewer defects compared to other suppliers. Alternatively, upgrading to an electronic ignition system can eliminate the need for a condenser altogether.

Starter and Bendix Considerations:

Your 6V starter will work with the 12V system, but there are a few things to keep in mind:

• Quick Engine Start: Ensure the engine starts quickly to prevent the starter from overheating.
• Bendix Mechanism: A 12V system may highlight issues with the Bendix mechanism. As it is now spinning at a higher speed. If you experience repeated Bendix failures, commonly the problem could be a bent pan or a bent starter shaft causing improper engagement. Resulting in the Bendix shattering.

Note: If your reason for converting to a 12V system is specifically that the starter is too slow to kick over the engine. Keep in mind that your starter might be warn out. Or that your engine might be too narrow a gauge starter wire If it looks like it has been replaced in the last 20 years. Commonly, off the shelf starter wires for modern cars are too narrow for older 6V systems. Choking the amps to the starter. Often the best source for a starter wire is one used on modern day Commercial Diesels. The larger wire gauge allows for more amps to get to the starter, unblocking the choke point of  power and thus helps to bring back some of that factory performance from your original starter.

Updating Gauges and Lighting: 

Gauges:

• Feel free to use your 6V gauges with a 12V system. The only thing that is mandatory is that you must install a voltage reducer in the gauge’s power circuit. They must remain at 6V. Or you could damage the gauges.

Lighting:

• Bulbs: Replace 6V sealed beams and bulbs with 12V equivalents. Many 6V bulb sockets can accommodate 12V bulbs with minor modifications, like filing down one of the bulb tangs.
• Alternative Bulbs: There are also 12V replacement bulbs designed to fit 6V sockets.

Heater Motor Replacement:

When upgrading to a 12V system, replacing the heater motor is not always necessary but it is recommended:

• Interchangeability: Early generation 12V heater motors are often interchangeable with 6V models from the same manufacturer.
• Adaptation: If a direct replacement isn’t possible, you may need to adapt a 12V blower motor to your heater case. Some manufacturers offer voltage reducers capable of handling 6V blower motors, but ensure they match your current requirements.
• BONUS TIP: If you convert over to 12V and you find that your system is draining the battery in just a day or two. The one thing that you might want to check is your cigarette lighter. As often the wires need to be reversed so that it doesn’t cause a parasitic draw.

Conclusion:

Upgrading from a 6V to a 12V electrical system can enhance the performance and compatibility of your classic car. By following these guidelines, you can make the transition smoothly while retaining much of your original equipment. If you’re considering this upgrade, make sure to consult with professionals and choose quality parts for the best results. If you are looking for a kit to help you with this transition check out .
1933-1941 Ford and Mercury Conversion Kits
Or
1946-1953 Ford and Mercury Conversion Kits
Or
Rebel Wiring – For a Complete Wiring Kits

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