So I couldn’t talk you into keeping you original electrical system 6 volts(see 6 to 12 Volt Conversion Part I). The following are points you will have to address in completing your conversion to 12 volts:

How am I going to create 12 volts of potential?

1.     Send your original generator out and have it re-wound for 12 Volts

2.     Buy a NOS  or used 12 volt generator

3.     Switch to an alternator

a.   One wire alternator (The engine has to reach 900-1400 RPM before many one wire alternators will begin charging. Most do not charge at idle!)

b.   Two or three wire alternator that uses an ignition excite circuit (has much better charge at idle speeds)

c.   You could consider our new PowerGEN alternators they look like the original generator and produce ~30 Amps at idle.

Do I need to change light bulbs?

All bulbs in the car need to be changed from 6 volt to 12 volt.

Here are some common 6 Volt bulbs and their 12 volt alternate parts:

6 Volt Part Number	12 Volt Replacement
51	53
55	57
63	67
64	68
81	89
82	90
87	93
88	94
1129	1141 or 1156(brighter)
1133	1143
1154	1157
1158	1176

When changing a bulb you need to consider the candlepower(brightness), Globe size and base. Some bases have pins that are on the same level (equal J-slot) and some are staggered (unequal J-slot).

What other electrical components do I need to change from 6 to 12 volts?

1.     All circuit breakers - sometimes attached to a switch or standing alone.

2.     Horn relays - it is possible to use a voltage reducer on the switch terminal of the relay. The points should be able to take the voltage.

3.     Overdrive Relay - same workaround as the horn relay

4.     Voltage Regulator - if using a generator

5.     Heater/defroster motors - you can use a voltage reducer here as well

6.     Electrical gauges i.e. Engine temperature, gas gauge, oil pressure.  - these gauges can be rebuilt to work with 12 Volts at a reputable gauge shop or you can use a voltage reducer on the power side of the gauge.

7.     Change all fuses in the car - replace all the fuses with ones with a lower amperage rating. When you double the voltage you cut the current (the amount of electricity actually flowing through the circuit) in half. You can apply this to which fuses you select.

8.     Most classic cars have a thermostatic relay built into the light switch. The old 6 volt light switch should work but it may not provide adequate protection. Consider replacing the circuit breaker on the switch, replacing the switch, or adding some extra protection.

9.     Replace the starter.  - the 6 volt starter will work with 12 volts for a while (30-40 thousand starts) but it will eventually burn itself up.

My car was positive ground what problem does this pose?

1.     You must switch to negative ground if you use 12 volt equipment originally made for American cars

2.     12 volt positive ground regulators and relays can be found at many british parts suppliers. (Some British cars were positive ground all the way up to the mid 60’s)

3.     On most gauges you can simply reverse the wires to keep them from reading backwards. Some gas gauges however, will burn up if hooked up backwards and will require being rebuilt or replaced.

4.     The ammeter may read backwards. This can be corrected by running the wire through the opposite direction on loop type ammeters or switching wire locations on the back of a full flow ammeter.

What about the wiring?

A 6 volt system actually draws more current than a 12 volt system. Therefore, the original wire is now thicker than it needs to be. You can always go bigger with wire but not smaller. You may need to modify an original harness to work with an alternator.  However, if you buy the wire harness from YnZ’s we can custom build it to fit your application.

There are a few other tricks that people have used to convert to a 12 Volt system. We do not recommend these methods.

Use two six volt batteries in series with a battery isolator.

Use a 6/12 battery - it has 3 posts: negative, +6Volts and +12Volts

Add a SECOND alternator for charging a second 12 Volt battery.

I hope this has been useful. We take a lot of calls at YnZ’s from people who tried to convert their car to 12 volts and forgot something. We help a lot of people out with burned out gas gauges! Just make sure if you are converting the car to 12 volts that you weigh all the options and make sure you didn’t leave anything out.