Test Lamp/Voltmeter

Use a test lamp to check for voltage. A Test Lamp (J 34142-B or equivalent) is made up of a 12-Volt light bulb with a pair of leads attached to grounding one lead, touch the other lead to various points along the circuit where voltage should be present. When the bulb goes ON, there is voltage at the point being tested.

A voltmeter can be used instead of a test lamp. While a test lamp shows whether or not voltage is present, a voltmeter indicates how much voltage is present.

An increasing number of circuits include solid state control modules. One example is the Electronic Control Module (ECM). Voltages in these circuits should be tested only with a 1O-megohm or higher impedance digital voltmeter or multi-meter (J 34029-A, J 39200 or equivalent.) Never use a test lamp on circuits that contain solid state components, since damage to these components may result.

When testing for voltage or continuity at a connection, you do not have to separate the two halves of the connector. Unless you are testing a "weather-pack" connector, you should probe the connector from the back. Always check both sides of the connector. An accumulation of dirt and corrosion between contact surfaces is sometimes a cause of electrical problems.