Tried a new trick with a Klein voltage tester on a tricky three-way switch

I was troubleshooting a messed-up three-way in an old house in Portland last week. Instead of my usual method, I tried holding the tester near the traveler wires with the switches in different positions. The LED lit up faintly on a wire I thought was dead, which saved me from pulling a bunch of wall plates. I learned that stray capacitance can give you a ghost reading if you're not careful. Has anyone else run into a phantom voltage reading that actually pointed them in the right direction?

3 comments

3 Comments

thompson.nathan1mo ago

That faint glow isn't always a trap, it's just a different kind of clue. You have to read the brightness. A solid glow means a real hot wire, but a faint one like you saw just shows an induced voltage from a parallel wire. It told you which traveler was still connected at the other switch. @riveradams is right about interference, but in a three-way, that ghost signal has to come from somewhere close. It pointed you to the right wire because the capacitance was coming from the other switch leg.

joelh641mo ago

Honestly, that faint glow sounds more like a ghost in the machine than a real clue. Those testers are so sensitive they'll pick up a field from a wire in the next room. I've chased that faint light before and it just led me to a dead end, literally. It's neat when it works out, but I wouldn't bet my afternoon on it. You probably got lucky more than anything.

riveradams1mo ago

Totally agree, that faint glow is a total trap. Remember chasing a flicker in my old apartment, turned out it was just interference from the neon sign at the pizza place downstairs. You can waste hours mapping a phantom signal that leads right back to your own fridge. Sometimes the tool is just too good, picking up every little bit of noise in the walls.