The Stovebolt Site Forums The Shop Area The Electrical Bay Question about external resistor on coil

Hey guys, Iv got some questions about my 1954 3100. Try to bear with me because the truck was a recent purchase and I’m still trying to figure out what has been changed, and electrical is my weak department. So this 54, the guy told me it’s updaed to 12v but I’m not sure what all was done for that update. It has a 12v battery, coil, generator. Right now I’m in the process of replacing the ignition. I rebuilt the distributor and got new plugs and wires etc. my question here is about the coil. The coil that was on it is labeled part number 27470, and says use with external resistor. I bought the truck it had a wire running from the key ignition to an external resistor, then a wire from the other side of the resistor to the coil. Then from the coil to the distributor. The coil that I’m replacing it with is a spectra c-660 12v. The spectra doesn’t say anything about using an external resistor. So my two main questions are does this coil still need an external resistor or can I run the wire from the ignition key straight to the coil? An my second question, is do I need any sort of resistor between the 12v coil to the distributor? My distributor is still running the stock points and condenser. Please help me try to decipher this puzzle! Thank you guys very much!

Iv been researching around throughout the day and here’s what I’ve found. The wire that goes from the key to the ballast resistor, and then the resistor to the 12v coil is correct. That lowers the 12v power down so I don’t burn up my points. However, what was missing on my truck. The starter solenoid has a side terminal, which should also be run to the ignition coil to give me 12v starting power. So all this time Iv been starting the truck on the lesser power through the resistor. So Iv ordered a new starter solenoid with a side terminal, and a new ballast resistor since the old one has seen better days, and I will give this a shot.

Sounds like you are on the right track.

Just updating this thread for anyone who comes across it with a similar problem. When converting to 12v, you need to add a ballast resistor before the coil to knock down the power, since your points can’t handle the 12v power. However, your stater button may or may not have an extra side terminal. If it doesn’t then get one on rockauto for about $20, and switch it out. That side terminal gets wired to the coil, giving you 12v power to the coil during starting, but once you let off the starter that side terminal no longer engages and you go back to your lessened power through the resistor. If you need help with any of this, there’s a tech article on this website with instructions on switching from 6v to 12v!