points wiring

[ray_mcavoy]

^ Ditto.

Some coils are printed with a message such as: "Use with external resistor". But if that is missing, worn off, or you just aren't sure, you can use a multimeter (set to the resistance / Ohms scale) to measure the coil's primary resistance. Just hook the meter's leads to the coil's (+) and (-) terminals without any other wiring attached. A stock GM Delco coil (or equivalent replacement) will most likely read somewhere around 1.8Ω and require an external ballast resistor. But some coils have a higher primary resistance (around 3Ω or so) and can be used without an external resistor.

The factory wiring (in most cases) also incorporated a wire that would temporarily bypass the ballast resistor to feed full battery voltage to the coil for a hotter spark while cranking the engine. That can be duplicated by simply running a wire from the starter solenoid "R" terminal to the positive coil terminal.