Please help!! 1971 340 duster having major ignition wiring headaches.
While the starter motor is running battery voltage gets pulled down. With a strong battery it will be around 11 Volts, and with high load or a weaker or old battery it may be 9.5 Volts but still start. Under 9 volts it probably won't start even with points ignition. Measuring the voltage at the battery with the starter motor turning is a way to test battery condition.
What is needed and useful is to know is which wire or circuit is being measured.
Choices are:
Run Circuit (labled on the diagrams as Ignition J2 and usually a blue wire) This supplies system power from the key switch when the key is in run.
Ignition Start (labled as Ignition J3 and is usually a brown wire). This supplies power from the key switch when the key is in start.
The ignition start is crimped to the wire going to the coil.
When the engine is running. Power is supplied from the run circuit. When the ECU closes the connection, power flows through the ballast resistor and coil. The resistor reduces the current flow and a voltage drop across the resistor can be measured. No current flowing, no reduction of voltage.
With a 4 pin ECU, a single 0.5 ohm ballast resistor will work like this.
There will never be 12 Volts at the coil if everything is working correctly.
While the starter motor is running battery voltage gets pulled down. With a strong battery it will be around 11 Volts, and with high load or a weaker or old battery it may be 9.5 Volts but still start. Under 9 volts it probably won't start even with points ignition. Measuring the voltage at the battery with the starter motor turning is a way to test battery condition.
Means nothing. There's no way for any of us to know which side you plugged the wires into.
What is needed and useful is to know is which wire or circuit is being measured.
Choices are:
Run Circuit (labled on the diagrams as Ignition J2 and usually a blue wire) This supplies system power from the key switch when the key is in run.
Ignition Start (labled as Ignition J3 and is usually a brown wire). This supplies power from the key switch when the key is in start.
The ignition start is crimped to the wire going to the coil.
This suggests very little current is flowing through the ballast resistor.
When the engine is running. Power is supplied from the run circuit. When the ECU closes the connection, power flows through the ballast resistor and coil. The resistor reduces the current flow and a voltage drop across the resistor can be measured. No current flowing, no reduction of voltage.
With a 4 pin ECU, a single 0.5 ohm ballast resistor will work like this.
