See full version: Do you need a resistor with a 12 volt coil
The resistance of an ideal inductor is zero. The reactance of an ideal inductor, and therefore its impedance, is positive for all frequency and inductance values. The effective impedance (absolute value) of an inductor is dependent of the frequency and for ideal inductors always increases with frequency. more
Ignition modules vary in appearance from one application to another, but they all perform the same basic function. In ignition systems that use a hall effect sensor and an ignition module, the electrical current from the hall effect sensor is what activates the ignition module.
The external resistor coils were used to boost primary ignition voltage during starting (making starting faster/easier). During starting, the external resistor is bypassed; once the starter is disengaged, power to the coil flows through the external resistor.
To find out for sure, use a multimeter to check the voltage on the positive wire of the coil with the ignition on. You can test the resistance of the coil using a voltmeter and measure the Ohms (resistance) across the +’ve and –’ve terminals.
Connect one end of the spark plug wire to the large center terminal of the ignition coil. Connect the other end of that wire to the center terminal of the distributor cap. [links]
Look at the ignition coil. These coils have one large terminal for the spark plug wire that runs over to the distributor and two small terminals that supply power to the coil. [links]
Disconnect the black negative cable on the negative post of the battery. more
Connect the positive terminal of the ignition coil to the "On" terminal of the ignition switch. Connect the negative terminal of the ignition coil to the coil terminal of the distributor. here
Older-model cars used the 12-volt ignition coils to provide power to the spark plugs. These coils had very simple wiring. They usually required only three wires: the spark plug wire, the power wire and the ignition switch wire. Ignition coils of this type are usually a little larger than a soda can and are heavy because of the metal core and the field coil windings. These coils are also filled with oil for temperature control. more
Reconnect the negative battery cable to the negative post on the battery. here
The voltage reaching the coil may be 12 volts, or about 7 volts if the coil has a ballast resistor. Most electrical equipment works on 12 volts, but most modern cars have a resistor in the ignition system to assist starting. The coil in a ballast-resistor system is rated at 7-8 volts instead of 12 volts. here
If you have an accurate ohm meter, reading across the posts of a 12 volt coil should be about 3 ohms. A 6 volt coil is about half of that. It is not an exact number, but close enough that you can tell 6 from 12 volt. Or, doing what Tom says, a 12 volt coil will flow about 2 amps if connected to 6 volts.
To check your coil, ensure you have 12V going to the positive terminal. Once you confirm that is the case pull the wire out of the centre of the distributor and hold it a cm away from the distributor centre terminal. Have someone crank over the engine, and there should be a nice blue spark..
A 6 – volt starter will work just fine with 12 – volts.
How to Wire 12 Volt Coils
When a 6 volt ignition system is converted to 12 volts either a 12 volt coil must be installed or a resistor installed in the circuit to reduce the coil voltage to 6 volts. The resistor regulates the voltage, keeping it at 6 volts, allowing the original 6 volt coil to be used in a 12 electrical system. here
Turn on the multimeter and set it to the "ohms" function. here
An automobile ignition coil acts as a transformer, having a primary and secondary bundle of wires that create and send an electrical charge to the spark plugs, causing them to fire. While ignition coils will generally last for the life of a vehicle, faulty spark plugs or spark plug wires can send irregular voltage surges through the ignition coil, causing the coil to burn out. You can test a 12-volt ignition coil for effectiveness by checking the resistance of its wire windings with a multimeter.
Insert one of the multimeter's probes into the center opening of the coil, contacting the metal terminal inside the coil. Touch the second probe of the meter to the ignition coil's grounding terminal. The meter should read 6,000 to 15,000 ohms. If it does not, the coil's secondary winding is faulty.
Pull the main ignition coil wire, the one that leads to the distributor, off the coil. Disconnect the small grounding wire, attached to the side of the coil, with a wrench.
Disconnect your engine's main negative battery cable with a wrench.