You can get a coil with a built in ressitor. that what i did when i had to redo something once never had a problem
Information about Ignition Coils - Certain ignition coils require an external ballast resistor (off any 1955-57 General Motors vehicle) or a full-length resistance ignition wire (off any 1958-74 GM vehicle) to prevent from putting too much voltage through the primary circuit and ignition points, which could burn them up. A ballast resistor or resistance wire is basically a voltage reducer that reduces 12 volts down to anywhere between 6-9 volts, depending on the load. (The ballast resistor shown here is the same used on the 1955-57 GM vehicles.) But if a coil reads "12 VOLTS" on its casing, then it has a built-in resistor. A resistor may not be needed with many new coils because most of them nowadays have a built-in resistor. And using a resistor doesn't effect the voltage output of a coil. It only prevents from burning it up, and it saves wear on the ignition points. The reason manufacturers don't install a resistor inside some high-performance coils is because these coils draw more amps from the battery. This causes the resistor to operate at a higher temperature, which could overheat and damage the windings within the coil. If you prefer to use a high-performance coil, when you purchase one, be sure to ask the salesperson if it has a built-in resistor or if it requires an external one. This is important for the life of the coil.
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