Fundamental of electrical automotive engineering - Test Lamp

Fundamental of electrical automotive engineering - Test Lamp. Fundamental of electrical automotive engineering. There are two basic types of test lamps : 12 volt, and self-powered. The 12 volt test lamp tests points in a circuit for available power. The 12 volt test lamp has no power of its own, and illuminates from power in the circuit being tested. The circuit must be ''live'' and have sufficient voltage and current to illuminate the 12 volt bulb. Circuits with high resistance may not illuminate the lamp. The self powered test lamp tests circuits or parts of circuits for continuity. It has a 1.5 volt or 3 volt battery and bulb in the handle. The bulb will illuminate when there is complete circuit through both contacts of the test lamp, and resistance is low enough to permit the bulb to illuminate.

Types

12 volt Test Lamp

The 12 volt test lamp can be used as a quick check for power by grounding the alligator lead and moving the test probe from connection to connection in the circuit. The 12 volt test lamp is not sensitive to polarity, so either termination can be grounded. In the example below, the 12 volt test lamp is probing various points in this circuit. See where the bulb illuminates and where is does not.

When testing for a short circuit to ground, the 12 volt test lamp can be subtituted for a blown fuse. The test lamp can be limit current in the circuit to a safe level. See the example below. If the bulb illuminates with all load devices in the circuit disconnected, this indicates a short to ground. Circuit connectors can then be disconnected, working back from the load devices until the test lamp goes out. The short is located between the last two connectors that were disconnected. See the above ilustration.

Self-Powered Test Lamp

The self-powered test lamp performs a basic test for continuity like an ohmmeter. The self-powered test lamp can also be useful when checking for shorts to ground. Like yhe 12 volt test lamp, the self-powered test lamp is not sensitive to polarity unless a component such as diode is present, so either termination can be grounded. The self-powered test lamp should be used to test only unpowered parts of a circuit. See the example below. If the self-powered test lamp illuminates when connected across a component or section of wire, then there is continuity. The bulb will not illuminate unless there is sufficient current present. Circuits or parts of circuits with high resistance may not illuminate the lamp.

Safety Information

This is the safety information can help you to avoid injury or damage to the vehicle.
Do not use test lamps in low-level circuits that have computers, processors, or control module. The current draw of the test lamp may damage the circuit or components. Test lamps can be used to verify the integrity of the battery and ignition power supplies and the grounds to computers, processors, and control modules.
Never pierce insulation with a test lamp probe, especially where the wiring may be exposed to weather. punctures in the insulation will permit moisture to be drawn in the cause wire corrosion.
A self-powered test light must be used in an unpowered circuit. If a self-powered test light is connected to a live 12 volt circuit, the 1.5 volt or 3 volt bulb will burn out.


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