To check an ignition switch, you can follow these steps:

1. Make sure the key is in the "off" position and the battery is disconnected.
2. Remove the cover from the steering column to access the switch.
3. Use a multimeter to check the continuity of the switch as you turn the key through each position (off, accessory, on, start).
4. If the switch fails to provide continuity in any position, it may be faulty and in need of replacement.

It's important to note that the specific procedure for checking the ignition switch may vary depending on your vehicle's make and model. It's always a good idea to consult your vehicle's service manual for detailed instructions.