ASE PREP: Test Lights another segment from my BAR Specific Diagnostic / ASE Course
The automotive test light is a low resistance probe with an internal bulb. The test light relies on circuit power to operate, as you probe the insulated side of a circuit the bulb should light. Using this light is a quick way to find a open circuit.
The down fall of a test light is, that it is dangerous on solid state control circuits. A technician should never use a test light on a solid state control unit unless directed to do so by a flow chart. The test light is a low impedance unit that will increase the current flow and damage the solid state unit. Trust me, I know, boy do I know, after burning up two computers back in the day, I finally got the point.
Use a test light to check fuses, not computer components! Unless you know the resistance or current that will flow through that light.
There are several different types of Test-Lights or Test lamps on the market today, the external powered light. This has a bulb in its handle with a alligator clips on the other end. This light relies on circuit power for operation.
You can check for a ground just as easy, connect the alligator clips to a power source and probe the ground, if the light or bulb comes on the ground is present.
Remember this procedure cannot tell you how much voltage is present or if there is resistance in the circuit.
ASE PREP: Test Lights and Solid State Devices
Solid State Devices can be damaged by some test lights, the test light will add an additional load to the circuit and draw more current.
In most cases, test lights are usually for checking fuses unless there is a flow chart that directs you to use a test light on a PCM Circuit.
Some test lights will increase current in a circuit, this can damage a Power Train Control Module “PCM” or if your lucky will just shut down to protect its self.
Self Power Test Lights:
Self power test lights check for continuity through a wire or component, they draw current from its own battery.
Any circuit being tested with a self power test light must be disconnected from its power source.
Again, this test light can not be use for checking resistance or the amount of voltage in a circuit.
NEVER CONNECT A TEST LIGHT TO A COMPUTER CIRCUIT UNLESS DIRECTED TO DO SO BY USING A MANUFACTURES FLOW CHART