With the advent of electronic ignitions and computer driven fuel injection, plus an increasing myriad of leisure and safety devices soaking up battery current, a strong dependable electrical system for your vintage or classic car is essential. This is especially true for vehicles driven to shows; participating in cruise-ins, or are daily drivers.
In 1956 Chrysler Corporation switched its line up to an industry standard 12 volt, negative ground system (Imperials had employed this system previously). Compounding the problem is the fact that Chrysler previously used a 6 volt positive ground system. Fortunately, a relatively simple solution is available. The following applies to Chrysler product vehicles from post war to 1955.
Those interested in maintaining an original factory appearance, the original 6 volt wiring harness, if in good repair, is sufficient to handle a 12 volt load. A complete harness can be substituted, from a parts car or an aftermarket supplier (recommended). We will concentrate on using OEM parts for our conversion.
With very few exceptions, all Mopar starters, generators, regulators, and relays from post war through the early 1960’s are MECHANICALLY interchangeable, with regards to flathead and OHV motors. For example, the starter motor from a 1957 V8 (12v) will bolt into a pre 1956 V8. For the conversion, simply install a 12 volt battery, being mindful of the negative (-) ground. Starter, generator, regulator, ignition coil, horn relay, horns, headlight relay, and all light bulbs can be replaced directly with 12 volt items. The distributor can be swapped out with one from the parts vehicle with the addition of an in-line ballast resistor. An alternative is to rebuild the original distributor using 12 volt rated points and condenser. There are also a number of quality electronic replacement units that fit within the distributor resulting in a completely stock appearance.
Electrical accessories are trickier. If using original gauges, simply reverse the leads for proper reading. (A condenser can be employed if the AMP or generator gauge reads erratically.) A new 12 volt gas sending unit is recommended, however the use of an in-line drop resistor is possible. Original power accessories such as windows, seats, antenna, etc. can also benefit from the use of commercially available 12 to 6 volt dropping resistors, after the leads to the device have been reversed at the switch.
Because of the design and nature of vintage radios, swapping grounds and/or the use of resistors is not recommended. Again, several aftermarket manufacturers have radios that bolt directly in place, including some which replicate the looks and functions of the OEM piece. There are also 12 volt batteries conforming to the size, shape and appearance of their original 6 volt counterparts. Some have 6 volt taps. Finally, the vehicle’s fuses need to be upgraded.
Most pre 1956 Chrysler products employed a vacuum driven windshield wiper system. If an electrical unit is encountered a replacement motor should be used. Alternatively, the original unit’s motor can be rewound by an electrical shop to 12 volt specifications. This is also true of starters, generators and other motor driven devices. This is an effective, albeit costly method for solving the 6 volt – 12 volt dilemma.
Be sure to use the proper gauge wire for the electrical load in question. And you should always bench test any planned electrical modifications before final installation. When questions arise, consult with a certified automotive electrical technician.