I assume that you are referring to the "ballast" resistor between the + lead of the coil and the Ignition lead on the key switch. At least that is where it goes on a '58 GMC truck. Assuming stock ignition, the ballast resistor is very important. With the key in the "start" position the ballast resistor is bypassed allowing 12 volts to the coil + terminal for a hotter spark during cranking. Once the engine starts and you let go of the key, the 12 volt source is removed from the coil + and the ballast resistor takes over. It limits current and voltage to the coil + terminal to around 6 to 8 volts when the points are closed. While the spark isn't quite as strong, the points last a lot longer.
It Is Worth Your While To put a voltimiter on the ' + ' side of the ignition coil and observe the voltage both with the engine running (7 ~ 9 VDC) and whilst cranking the starter ~ then it should jump up to battery voltage and vary as the engine cranks . If it doesn't jump up to 12 volts when the starter operates , there's a problem that needs fixing and once fixed it'll start easier .
The ballast resister is located in line with coil to dissapate heat that would otherwise be generated in the coil. It is connected to the firewall on the raised bump to allow for better cooling. Yep, it is needed.
