1955 Ignition Coil Wiring

[calbears]

The coil on my '55 (6V positive ground) was not producing enough spark making the car hard to start. I removed a red wire from the "+" side of the coil that came from the fire wall. I removed another red wire from the "-" side of the coil that went to the distributor. I installed a new coil and hooked up the red wire from the firewall to the "+" side and the other red wire coming from the distributor to the "-" side. The car starts immediately upon turning the key. The car has never started better.

Two issues: First, I had not noticed it when I first removed the red wire coming from the firewall to the "+" side, but wrapped with that red wire was also a brown wire. When I first removed the two red wires the brown wire was not attached to the coil, or anywhere else as far as I can tell. Again, the car starts great but seemingly the brown wire needs to be attached somewhere. Where would that somewhere be?

Second issue: In reading a 2022 post on this cite regarding the ignition coil on a '55 6V positive ground, the consensus was that the red wire from the firewall should be attached to the "-" side of the coil and the red wire from the distributor should be attached to the "+" side of the coil. So, it sounds as if I have the two red wires backwards. Should I switch them? And again, where would the brown wire go? If the wires should be switched and the brown wire is not even connected to the coil, why is the car even starting? Will the backwards wiring cause damage to the coil? It sounded like the person starting the coil post in 2022 had the wires switched and the car was going though coils every 500 miles. The coil I took out of my car that was not producing enough spark probably only has about 500 miles on it but that 500 miles was over the last 30 years.

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[Tom Alpers]

If they are hooked up backwards to the coil I'm not sure it would even work. Not sure of that part, I'd need to look at a wiring diagram. On the 55 the wiring for the coil is different than for the 56, 57. As to the extra brown wire, it sounds like someone might have replaced the wring harness with a later one for a 12 volt setup. With 12v there are two wires to the + on the coil. One for starting which is a full 12v and it's connected to the I (ignition) terminal of the starter solenoid. It only has 12v when the engine is cranking. The rest of the time it has no power. The second wire is hot whenever the ignition swatch is ON. It goes to a ballast resistor which drops the voltage to about 9 volts for normal car operation after the engine starts. For your 55 the coil simply gets the full 6v all the time, there is no ballast resistor and no need for the second wire. Since you don't know what the second wire is hooked to I would not connect it, for all you know it is grounded and if you connect it to the red wire you might create a dead short. If, as I'm guessing, all or part of your wiring has been redone, it would be risking to base too much on wire color, who knows how the last guy did it.

 

[calbears]

Thanks. Tom.

doug7740 are you out there? I noticed that you replied to the 2022 post, “1955 Ignition Coil Issue,” and you have a ‘55. I believe I have the wires switched according to your reply back then. Do yiu have a brown wire and if so where does it go?, or is it for a 12V system as Tom mentioned?

 

[doug7740]

calbears,

My 1955 Thunderbird is 6 volt, positive ground. Because of this the red/green wire from the ignition switch is connected to the negative terminal of the coil and the black wire from the distributor is connected to the positive terminal of the coil. If your car has overdrive there should also be a white/red wire from the negative terminal of the coil to the overdrive kickdown switch.

Attached is an article from the January/February 1997 Earlybird magazine which explains the polarity of the coil.

doug7740
1955 Thunderbird Blue

 

[calbears]

Thanks for replying as you have several times over the years.

I want to make sure I’m reading your response correctly. I’m reading that there is one wire coming from the ignition and that wire is red with a green stripe?, and that one wire goes to the negative side? I want to clarify that there are not two wires, a red wire and a separate green wire coming from the ignition where both would connect to the negative side.

The car does not have overdrive so I don’t know what the brown wire is. Maybe it’s for a 12V system as Tom suggested.

 

[calbears]

Doug, disregard my last post. For some reason I did not see the article that you attached. Thank you. That was a great article that explained it perfectly. Additionally, I found in my stack of TB materials the wiring diagram for the ignition. It was just as you described, including the colors of the wires. As the article said, if the wires are hooked up backwards, the car may still function (which it does), but it's not good for the car or the coil. Most likely the reason the guy from the 2022 post was going through coils every 500 miles. Anyway, thank you again. Your knowledge, expertise, and willingness to help the rest of us out are greatly appreciated.