#### TEST LIGHTS

The test light is used to check circuits and components while electrical current is flowing through them. It is used for voltage and ground tests. To use a 12 volt test light, connect the ground clip to a good ground and probe wherever necessary with the pick. The test light will illuminate when voltage is detected. This does not necessarily mean that 12 volts (or any particular amount of voltage) is present; it only means that some voltage is present. It is advisable before using the test light to touch its ground clip and probe across the battery posts or terminals to make sure the light is operating properly.

WARNING
Do not use a test light to probe ignition spark plug or coil wires. Never use a pick-type test light to probe wiring on computer controlled systems unless specifically instructed to do so. Any wire insulation that is pierced by the test light probe is a good candidate for failure. Most vehicle manufactures recommend against this, some also recommend against back-probing. Back-probing is where the tip of the probe is forced into the back of the connector. Refer to the specific vehicle manufacturers for recommendations.

Like the jumper wire, the 12 volt test light is used to isolate opens in circuits. But, whereas the jumper wire is used to bypass the open to operate the load, the 12 volt test light is used to locate the presence of voltage in a circuit. If the test light illuminates, there is power up to that point in the circuit; if the test light does not illuminate, there is an open circuit (no power). Move the test light in successive steps back toward the power source until the light in the handle illuminates. The open is then between the probe and a point which was previously probed.

The self-powered test light is similar in design to the 12 volt test light, but contains a battery in the handle. It is most often used in place of a multimeter to check for open or short circuits when power is isolated from the circuit (continuity test).

The battery in a self-powered test light does not provide much current. A weak battery may not provide enough power to illuminate the test light even when a complete circuit is made (especially if there is high resistance in the circuit). Always make sure that the test battery is strong. To check the battery, briefly touch the ground clip to the probe; if the light glows brightly, the battery is strong enough for testing.

NOTE: A self-powered test light should not be used on any computer controlled system or component. Even the small amount of electricity transmitted by the test light is enough to damage many electronic automotive components.

Fig. 1: Test lights are simple to use, however check manufacturers recommendations before probing any wires or connectors.