ignition coil ballast resistor

Bill Goddard

Bill Goddard

Well-known member
I have tried to search this question but no results. I have a 12v system on my four-door leatherback. I am trying to choose the proper coil. I have a 12v coil that says it has a resistor built in. The ohm reading across the terminals is 3 ohms. I understand a 6v coil should read 1.5 ohms so I think 3 ohms is right for a 12v coil/ 12v system. This would mean the 12v coil would deliver the same amperage as a 6v coil. Am I right? Thanks for any help Bill Goddard
 
You are correct.

Another option is to take the 6 volt coil, that reads ~1.5 ohms across the primary, and add a 1.5 ohm ballast resistor to the power feed wire going to the coil. Those 2 together (in series) will then measure 3 ohms and work well on 12 volts. Having that extra 1.5 ohm resistance inside or outside the coil doesn't change how it operates. This lets you keep the original 6 volt coil, instead of buying a new 3 ohm coil.
 
I appreciate all the responses above. They have cleared up the question for me. Oddly, I have a 12volt coil labeled as "super hot " that measures 1.5 ohms so I installed it with a 1.5 ohm ballast resistor. The resistance now measures 3 ohms on a 12v coil. It seems to be working. Bill Goddard
 
This is basically what auto manufacturers did after they switched the cars over to 12-volt systems back in the 50s. Some manufacturers used the wire wound ballast resistors and some used the resistor wire clear up into the early 70s.
 
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