Not getting 12 volts to coil
Lets look at the two wire junction on the resistor for a '70 Barracuda:
When Starting, voltage at that terminal should be the same as the battery voltage. If the battery drops to 11 Volts during starting, then the voltage at that side of the ballast resistor should be 11 volts. If its 9 Volts at the battery, it should be 9 volts at the ballast connection.
During start, only about 5 amps flows from the junction at the starter relay to the starter switch, where it divides into two smaller currents. There should be no resistance to that flow.
When the engine is running, voltage at the ballast resistor's two wire junction should be less than at the single wire terminal.
Voltage at the single wire terminal should be the same as the power supply voltage.
Why?
With the key in run, current to the coil and points must flow through the ballast resistor. Current flowing through resistance loses voltage. When the coil sees less voltage, it draws less current. Together this provides the correct amount of electricity for the coil to function as designed.
If we want to know what voltage the regulator sensing terminal is seeing, we need to measure the at the ballast resistor's terminal with the single blue wire. Another place to check is at the alternator's blue wire field terminal connection.
Lets look at the two wire junction on the resistor for a '70 Barracuda:
When Starting, voltage at that terminal should be the same as the battery voltage. If the battery drops to 11 Volts during starting, then the voltage at that side of the ballast resistor should be 11 volts. If its 9 Volts at the battery, it should be 9 volts at the ballast connection.
During start, only about 5 amps flows from the junction at the starter relay to the starter switch, where it divides into two smaller currents. There should be no resistance to that flow.
When the engine is running, voltage at the ballast resistor's two wire junction should be less than at the single wire terminal.
Voltage at the single wire terminal should be the same as the power supply voltage.
Why?
With the key in run, current to the coil and points must flow through the ballast resistor. Current flowing through resistance loses voltage. When the coil sees less voltage, it draws less current. Together this provides the correct amount of electricity for the coil to function as designed.
If we want to know what voltage the regulator sensing terminal is seeing, we need to measure the at the ballast resistor's terminal with the single blue wire. Another place to check is at the alternator's blue wire field terminal connection.
