One of my troubleshooting maxims is to make all AC voltage measurements with a loading meter (LoZ on a Fluke or a "Wiggy" solenoid voltage tester). The reason for this is avoid getting head-faked by ghost voltage. This short video explains what ghost voltage is and why we, as professional technicians, need to be aware of it when troubleshooting. I also show a clear example of ghost voltage in a live circuit and how that could at least have you scratching your head during troubleshooting.
Understanding basic electricity, circuits, appliance technology, and troubleshooting techniques are the core skills we teach in the Core Appliance Repair Training course and should be part of every tech's mental toolbox. If you know the fundamentals, you can figure out the most problems. Learn more, earn more!