View Full Version : Electrical: Ignition resistor

07-20-2017, 07:43 PM
I have a 1954 sedan and I have installed a 1963 259, the sedan is 6 volts and the engine was originally 12 volts, however I have converted the engine to 6 volts. In reviewing the wiring diagram for the sedan there appears to be no resistor or by-pass system for the ignition. The 63 259 used a pink resistor wire from the ignition switch to the coil and a by-pass system. Looking at a 1956 wiring diagram a balast resistor and by-pass system is introduced only for the v-8 models. There is no resistor for the 6 cylinder models. Why does the V8 model have a resistor/by-pass and not the 6 cylinder? What would be the consequences if I did not use a resistor/by-pass system on the conversion I have installed. Does the resistor system only apply to 12 volts with negative ground?, as that is when it was introduced.

07-20-2017, 08:09 PM
The resistor is not used on 6 volt systems. It was added in '56 with the change to 12 volts.

07-20-2017, 11:13 PM
There is no need to reduce the Voltage on a 6 Volt System, it's already only 6 Volts, how LOW can you go! :D

07-21-2017, 01:22 AM
In the wiring diagram I was looking at for 1956 the resistor only applied to the V8 engines not the 6 even though they were both 12 volts.

07-21-2017, 02:07 AM
If the car is still a 6 volt, 1954, you should use the 54 wiring diagram.

Jeffry Cassel
07-23-2017, 09:08 AM
The purpose of the resistor or a pink resistor wire is to drop the voltage coil. 12 volts will cause the points to burn out rather quickly. If you have a 6 volt system none of this is needed; if installed I'm not sure it would run on 3 or 4 volts.

07-23-2017, 12:22 PM
Still part of my question was, the diagram indicated a resistor for the V8 but not for the 6 cylinder with both systems being 12 volts.

07-23-2017, 06:23 PM
The 6 cylinder engines used a coil with an internal resistor so instead of having around 1.5 ohms resistance on the coil primary winding, the 6 uses a 3 ohm coil. Chrysler did this on their 6 cylinder engines and most of the import cars with a Bosch electrical system also used a coil with an internal resistor. Bud

07-24-2017, 12:20 PM
Thanks Bud that helps explain that. Was there a bypass to supply the full 6 volts for starting?

07-24-2017, 01:35 PM
this topic is interesting to me....I have two 12v vehicles in which I used resistors and the bypass's. However, on my '39 Stude...just to move the car and to "yard drive it", I am using a 12 volt coil but with a 6 volt battery, and it runs just fine! Would this work just as good as a 6 volt coil without a resistor? (assuming the 12v coil did not have internal resistor).

07-24-2017, 05:52 PM
A 12 volt coil will work on 6 volt system but the the coil primary winding resistance in a 6 volt system is around 1 ohm and a 12 volt coil using an external resistor has a resistance around 1.5 ohms. When using a 12 coil on a 6 volt system you can expect a lower output voltage. On 12 volt systems using a ballast resistor, there is a resistor bypass built into the starter solenoid to momentarily supply full battery voltage to the coil when the engine is cranking which will produce a faster start. 6 volt coils with the exception of some 40's Fords do not need a resistor on the hot side of the coil as the voltage is low enough to keep the points from burning up in a short time. Bud

07-24-2017, 06:12 PM
thanks Bud ..the ohms explanation makes sense. I understand the bypass...as I was told..the starter draws so much that the volts going to the coil is reduced , therefore which may keep it from firing off. I have seen this on my '51 ford and VW...the starter spins and spins but will not fire up until the moment the starter is released. Thats why I have a bypass now to keep 12 volts on the coil during cranking.
but back to altair's comment #9...on 6 volt systems... Is it fair to say even when a 6v starter is spinning, the reduced voltage to the coil does not significantly impact the coil's operation...therefore no need for a bypass? btw...I have never seen a bypass on a 6 volt system.
If I wanted to replace my 12v coil with a 6v...will all 6 volt coils have 1 ohm? (if I were to have a generic 6v coil laying around)

07-25-2017, 08:37 AM
All of the 6 volt coils I have tested have a primary resistance of 1 ohm. That doesn't mean that all 6 volt coils have the same resistance. I don't recommend replacing a 12 volt coil using an external resistor with a 6 volt coil as the lower primary resistance of the 6 volt coil will draw too much current through the points causing shortened life. Any time the voltage is reduced to the primary winding of an ignition coil the voltage available on the secondary winding will be reduced. 12 volt coils when operating through the ballast resistor will see 9 or 10 volts on the primary winding with the engine running which keeps the current flowing through the points at an acceptable level. 6 volt coils do not need any sort of bypass because the voltage is low enough to keep the current through the points at an acceptable level. Bud

07-25-2017, 09:47 PM
hey Bud...I'm not changing my 12v ford or my 12v vw to a 6 volt coil...would never do that... but on the studebaker ....since it has the 6 volt battery, I will be changing the 12v coil on it now to a 6 volt coil so it will be correct. That 12v coil just happened to be on the car when I put the 6 volt battery in it.
I was just wondering if there were different ohm ratings for 6v coils and what should I look for ....or if all 6 volt coils were the same. Sounds like they all might have the same resistance. I may have a VW Bosch 6v coil laying around somewhere... if I can just find it.