The Ford Barn

rotorwrench · 12-21-2025, 10:17 AM

The ignition/starter switches control multiple separate circuits. The start circuit to the solenoid and the ignition circuit to the coil, BUT, as was mentioned, there can be a ballast bypass circuit to allow 12-volts to the coil only during the start phase and then back to reduced voltage after the start function is released to run position. The start relay usually controls the bypass function. There is a circuit for the instruments as well. The ignition switch also provides power to the generator light if so equipped. The voltage regulator cut out pole is what opens that circuit after the generator comes on line. These other parts of the switch could have an effect on the ignition circuit if there is an open or short anywhere in the run circuits of the switch.

Bypassing the switch to the coil should be run through the ballast resistor to drop the run voltage to the coil. A 1.5-Ohm coil will work on 12-volts but the current is too high for anything but momentary operation. All components and wiring can be checked with an Ohms meter but the circuits have to be isolated for each wire. Checking voltage on a circuit with a resistor can be in question to the average mechanic. Voltage has to be checked across the resistor to catch the voltage drop otherwise it will always give system voltage if checked at the coil. Ballast resistors are generally around 1 to 1.5 Ohms if checked with an Ohms meter. The wires should give little or no resistance and should have infinity Ohms to ground. This is how you find a wire shorted to ground.

Another thing to consider is if the vehicle has an overdrive transmission. The Borg Warner electric OD transmissions have a kill circuit that is controlled by the kick down switch and the operating solenoid. It cuts power to the coil momentarily during kick down to insure the drop out of the overdrive solenoid. If there are shorts or component problems with this circuit, it may have a detrimental affect on the ignition coil function.

12-21-2025, 10:17 AM	#10
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 18,006	Re: testing a starter switch The ignition/starter switches control multiple separate circuits. The start circuit to the solenoid and the ignition circuit to the coil, BUT, as was mentioned, there can be a ballast bypass circuit to allow 12-volts to the coil only during the start phase and then back to reduced voltage after the start function is released to run position. The start relay usually controls the bypass function. There is a circuit for the instruments as well. The ignition switch also provides power to the generator light if so equipped. The voltage regulator cut out pole is what opens that circuit after the generator comes on line. These other parts of the switch could have an effect on the ignition circuit if there is an open or short anywhere in the run circuits of the switch. Bypassing the switch to the coil should be run through the ballast resistor to drop the run voltage to the coil. A 1.5-Ohm coil will work on 12-volts but the current is too high for anything but momentary operation. All components and wiring can be checked with an Ohms meter but the circuits have to be isolated for each wire. Checking voltage on a circuit with a resistor can be in question to the average mechanic. Voltage has to be checked across the resistor to catch the voltage drop otherwise it will always give system voltage if checked at the coil. Ballast resistors are generally around 1 to 1.5 Ohms if checked with an Ohms meter. The wires should give little or no resistance and should have infinity Ohms to ground. This is how you find a wire shorted to ground. Another thing to consider is if the vehicle has an overdrive transmission. The Borg Warner electric OD transmissions have a kill circuit that is controlled by the kick down switch and the operating solenoid. It cuts power to the coil momentarily during kick down to insure the drop out of the overdrive solenoid. If there are shorts or component problems with this circuit, it may have a detrimental affect on the ignition coil function.