Before starting work on T100 models, cleanly separate the negative battery cable and make sure the anti-theft audio system's lockout option is disabled if your vehicle has one. Before starting work, turn off the airbags, pull off the steering wheel and cover panel over the steering column. Pull these two parts off from in front of the Ignition Lock Cylinder, and take all the electrical wires out. Using an ohmmeter, check the continuity of the switch terminals: When using the test meter, you'll find no current if the key is in the LOCK position (no connections). With the key in ACC position, you'll see a link between terminals 2 and 3. Make sure there's no connection between the key unlock warning switch and the switch when it's off, and the key not present. Measure the switch's connections twice: first, with no current and no key, then, when the key is there and the switch on, there should be a flow between terminals 4 and 5. When the Ignition Lock Cylinder fails, you need to replace it.