I’m an avid DIYer. I never label parts and fasteners. I regret it every fucking time.

Don’t pierce wire insulation when taking readings or checking for power. Instead, use T-pins to back-probe wires. Slide the pointy end down into the connector, and attach your multimeter. A paperclip can work too, but the T is easier to fasten an alligator clip to, and the sharp point helps to minimize damage to the…