If you want to upgrade or restore your vintage or classic car made before the mid-80s, you’ll probably need a 6V to 12V conversion kit.
All vehicles, mopeds, and motorcycles currently run on 12-volt electrical systems, but there was a time when 6V was the standard.
Luckily, the upgrade process is relatively straightforward, and here’s what to and what not to replace.
What Is 6V to 12V Conversion?
This conversion process involves replacing the 6V battery with a 12V battery and the 12V components to match.
12V electrical systems are more efficient than their 6V counterparts because the higher voltage means you need a lower current (half) to run through the circuit.
The copper conducting core must be thicker in 6V systems because they transmit higher electrical currents through their wires.
The conversion process doesn’t involve replacing the harnesses because they are sufficient for the 12V components.
They are more than sufficient because they are thick enough to handle the 6V system.
What To Replace
These cars featured generators that produced electric current at 6V, and there’s no way to modify it to recharge a 12V battery.
Before buying the replacement, try to measure the total load of the system depending on the vehicle. For instance, a 55-amp 12-volt alternator is sufficient for a 1961-1966 VW Beetle.
Also, match the alternator pulley to the old one for compatibility purposes. Check the belt width, pulley diameter, and belt depth.
A car alternator
But finding a new alternator with mounts matching the old one is almost impossible. So, you should make new ones using a hand drill and bar stock, which you can buy from the hardware store.
You’ll also need washers or spacers to align the alternator pulleys with those connected using the serpentine belt.
And don’t throw away the original 6-volt system because you might think of restoring the vehicle to its original form later. Or you might sell the car to someone who wants it in its original condition, including the electrical system.
Voltage regulators regulate the alternator’s output to match the electrical load. Most modern alternators feature internal regulators, but the old units require external regulation.
An alternator’s voltage regulator
And the voltage regulator for the 6V system cannot work with a 12V alternator. So, you must replace this component with a 12-volt regulator. Alternatively, you can also look for an alternator with an internal regulator. But don’t throw away the old unit for the reasons described earlier.
The battery is the primary power source for the vehicle, and selecting a replacement requires multiple considerations. For instance, this 12-volt system battery should deliver the amps that match the vehicle’s electrical load, especially the starter motor.
A mechanic replacing a 12V car battery
Also, it should fit in the vehicle. So, match the exterior dimensions of the old 6V battery with the new one. Remember to reverse the cable connections if the vehicle has a positive ground system.
6-volt light bulbs and assemblies will burn out immediately when connected to a 12V system.
Therefore, you should replace these components if they are still in their original form. If on a budget, go for the rubber assemblies. Otherwise, steel case models are better.
On the light bulbs, replace the turn signal, license plate, tail light, dome light, parking, dash indicator, and headlights with 12-volt bulbs. You can install halogens, but LEDs will give you brighter headlights.
An LED car headlight
Fuses and Relays
The old car fuses have a higher amperage rating to protect electrical components in a 6V system. So, they won’t blow in this new low amperage system if any electrical faults pop up.
A car’s fuse and relay box
Remember to replace these components or the entire fuse box to handle the low-amperage circuits. To get the precise fuse rating, check the load in the circuit. For instance, the headlight fuse should match the rating of the new headlights you are installing.
Some vehicles had relays, and these should match the new 12V system. These include the headlight, horn, and flasher relays.
Old vehicles had vacuum-operated wipers, and you must replace this system with a 12V electric wiper motor.
Dashboard gauges are sensitive to voltage changes because they use voltage variations to adjust the needle position. These devices will become useless when you switch from 6V to 12V. In fact, they will burn out because the voltage will be double their rating.
A vintage car’s instrument cluster
Replacing the gauges is straightforward, but you’ll encounter size and shape compatibility issues. The new gauges might not fit or will look out of place.
You can keep the original gauges by installing a resistor or a DC-to-DC step-down converter. The converter option is better than the resistor because it wastes less energy as heat. But regardless, you should install one converter/resistor for each gauge.
Instead of looking for a solution to maintain the old radio, install a new head unit running on 12V. Not only will it be more efficient, but it will also have more features, such as USB and FM radio.
The stereo in a vintage car
But if you insist on maintaining the vehicle’s original interior, look for experts who do 6V AM radio restorations to work on the stereo. Like with gauges, this conversion process requires converters or resistors.
What You Can Keep
It is difficult to get a 12V starter replacement that matches the drive gears and mounts in your 6V system. So, you can maintain the device and use it as it is.
A starter motor in a vintage engine
This voltage mismatch is risky, but you can keep the 6-volt starter safe by avoiding cranking it for long periods. If you do, you’ll burn the motor. Therefore, you should maintain the engine to prevent the starter motor from overworking.
You have two options with the ignition coil. If within your budget, you can replace it with a 12V coil. But if the replacement coil is too costly, you can make the 6V unit compatible using a ballast resistor.
An ignition coil and distributor setup are connected using a high-voltage wire
However, you don’t have to change anything if your vehicle uses a magneto ignition. These magnetos are self-contained units and can run on 6V or 12V because voltage does not impact them.
Wire harnesses for a 6V electrical system have a thick core sufficient to transmit the lower amperage for 12V systems. So, you don’t have to replace this component.
But you might have to replace the stock wiring harness due to wear or aging. So, we recommend inspecting the wires before installing the replacement components.
You can fit in thinner wires for the 12V system because they are cheaper and are compatible with the thicker 6V cables. Remember to wrap the joints using heat-shrink tubing.
These devices are responsible for indicating the charging or discharging rate of the battery. You might only have to rewire the ammeter from the voltage regulator in some vehicles, but others require a complete replacement.
A vintage car’s instrument cluster with an ammeter
However, the ammeter will show opposite readings (discharging when charging and vice versa) if you do not reverse the 12-volt battery cable connections in a positive ground system.
Alternatively, you can switch the ammeter leads to match the negative ground instead of reversing the battery cable connections.
Restoring old cars is fun, but a critical thing you should be aware of is the 6-volt to 12-volt conversion. Some components can remain in the vehicle, but others have to go.