Test Light Instructions
Test Light Step 2 - Before staring any testing the test light itself must be tested, connect the clip or clamp to a known ground source, in this case the battery negative terminal is being used but almost any metal surface on the vehicle will work. Gently, touch the test light probe to a known power source, we use the battery positive is this example but any known power source such as a fuse or positive battery cable will work.
Testing the Test Light
Test Fuse Power Step 4 - When power tests okay for power at the source such as a relay or fuse, yet power is not present at a particular accessory such as the cooling fan a test light can trace the problem down through a process of elimination.
Burned Wiring Step 5 - Power must be present at the large terminal of the alternator to charge, a test light performs this task easily.