6 Volt to 12 Volt Changeover

By Stephen Kassis

The benefits of 12-volt charging systems over the earlier 6 volt systems are well established. It has been over 65 years since 12 volt systems became the automotive industry standard in 1955. So does your vintage car or truck really NEED to be changed to 12-volt? The answer is “Maybe”.

The main reason for the change to 12-volt was the increase in horsepower and compression ratios that caused hard starting. In Chevrolets, this began in 1953 with the increased compression ratios. When the engine was hot it would sometimes have trouble starting the car as 6-volt systems lacked the cranking power needed for the additional compression.

Engines prior to 1953 should not have this problem as long as a good battery and battery cables are present in the car or truck. Unless you will be driving your vintage car on a daily basis, we do not recommend changing your system to 12-volt if the engine is prior to 1953. Possible exceptions would be if you want to run 12-volt accessories such as a radio or special lighting like halogen headlights that are only available in 12-volt. Earlier engines with lower compression ratios do not require the additional boost of a 12 volt system. If you stay with a 6-volt system, you may be interested in our Voltage Inverter to change from 6-volt to 12-volt for radio or other low power accessories. For installation on negative ground systems – use part # CAS-1.

Some of the benefits of changing to a 12 volt system are easier starting, halogen headlights, LED tail lights, and one-wire alternators and more power for accessories like aftermarket radios & amplifiers. If you have decided to make the changeover to a 12 volt system, you must make several decisions. This article will outline items that need to be addressed and you must decide which will work best for your application.

  1. Coil & Ballast Resistor – Change the original 6-volt coil to a 12-volt – # FS-770. A ballast resistor is now required between the coil and the distributor. This will insure that only 6 volts reach the ignition points or they will burn prematurely. Ballast resistor is part # FS-1008.
  2. Drop resistors – Before hooking up 12 volts to your vehicle, you must protect the fuel gauge with a special resistor for this application – # FS-94. Also required is a large resistor for accessories like original 6-volt heater or radio – use FS-129 or FS-129R.
  3. Starter Motor – you can continue to run the 6-volt starter until the unit wears out. 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, you should change the starter to 12-volt – #’s R-3500-12 or R-3530-12.
  4. Generator or Alternator? – There is no question that an alternator will give superior performance to a generator system with a voltage regulator. The first option is 12-volt Generators #’s R-9005 or R-9010. You must also change the voltage regulator to a 12 volt unit – # OS-94 or OS-94R.

    The other option is to use an Alternator. We sell an internally regulated GM type alternator. The benefit to this type of alternator is that you do not need a separate voltage regulator. If you are planning to run halogen headlights, you must use an alternator as generators cannot keep up with the amperage required run halogen bulbs. Use part #R-7127-12.

    Also available is an alternator bracket kit that bolts onto your original 4 or 6-cylinder engine where the old generator was mounted –  TR-665 1926-1928; TR-666 1929-1936; FS-478 1937-1954 or FS-142 1955-1962. When using an alternator on 1926-1952 engines with wide fan belts, a special wide belt pulley is required – # VT-18.
  5. Turn Signal Flasher – If you have installed turn signals on your vehicle, the 6-volt flasher must be changed to a 12-volt flasher – # FS-453A or FS-453B.
  6. Horns – Most 6-volt horns will not work on a 12-volt system. We have two different replacement 12-volt horns: # FS-1014 is a GM style Hi-Lo Horn Set. Also available is an economy set of dual horns – AL-38. Both of these horn sets will require a 12-volt horn relay # FS-1007.
  7. Light Bulbs – From headlight to tail light and all lights in between, you must change all bulbs in the vehicle. Sealed beam headlight bulbs – # FS-321A or FS-321H; Dome, dash & tail light (original #63) – # FS-23A; Tail & Spot Light (original #1129) – # FS-22A; Dual contact parking & tail light (original #1154) – # FS-18A, FS-18AA or FS-18AR; Dash light (original #55) – # FS-273A; Dome light – single contact (original #1133) – # FS-1133A; Dome light – dual contact (original #’s 82 or 88) – # FS-493A; Indicator light (original #51) – # FS-884A.

Now for the good news… Most of the items needed to make the changeover from 6-volt to 12-volt are very simple to install. Anyone with a small amount of mechanical ability can install all of this easily over a weekend.