An ignition switch supplies voltage to the ignition control module and/or the ignition coil. Often an ignition sytem thas two wires connected to the run terminal of the ignition switch. On is connected to the module. The other is connected to the primary resistor and coil. The start terminal of the switch is also wired to the module.
You can check for voltage using either a 12-volt test light or a digital multimeter (dmm).
To use a test light:
- Turn the ignition key off and disconnect the wire connector at the module.
- Disconnect the S terminal of the starter solenoid to prevent the engine from cranking when the ignition is in the run position.
- Turn the key to the run position and probe the red wire connection to check for voltage.
- Check for voltage at the battery terminal of the ignition coil using the test light.
- Next, turn the key to the start position and check for voltage at the white wire connector at the module and the battery terminal of the ignition coil. If voltage is present, the switch and its circuit are okay.
To do the same test using a DMM:
- Turn the ignition switch to the off position and back-probe, with the meter's positive lead, the power feed wire at the module.
- Connect the meter's negative to a good ground at the distributor base.
- Turn the ignition to the run or start position as needed, and measure the voltage.
- The reading should be at least 90% of battery voltage.