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Knowledge is power; this knowledge can save you from wasting time testing good components or systems.

Once the fault list is formed, you can only remove an item from the list by asking the customer/service advisor questions to eliminate the item as a possibility or by testing the item to see if it is working properly.

Knowing what questions to ask can be difficult also. Sometimes you will have to read the operational description of the affected system, look at the wiring diagram, and try to find common points (power and grounds) that the affected system has with other normally operating systems to help you decide which questions to ask.

Sometimes you can use the process of deduction (to reach a conclusion by reasoning) to eliminate an item from the fault list. For example: If the radio in a vehicle does not work and the radio shares a power fuse with the horn relay; simply attempting to honk the horn will verify if the common fuse is good. If the horn does not honk, the fuse needs to be inspected, if the horn does honk, then you can deduce that there is no need to check the fuse.