Found a better way to test those old Korry switches

I was troubleshooting a stubborn annunciator panel on a King Air last month and kept getting inconsistent results with the standard continuity test. The manual said the switch should show open or closed clearly, but I was getting intermittent readings that made no sense. After about 45 minutes of frustration, I remembered an old trick a mentor showed me years ago. I put a 100-ohm resistor in series with my multimeter lead to limit the current during testing. Turns out the switch contacts had a thin layer of oxidation that fooled the standard test but the resistor trick let the higher voltage burn through it. Fixed the panel in under 10 minutes after that. Has anyone else run into this issue with these older illuminated switches on turboprops?

2 comments

2 Comments

hugoj121mo ago

Haha yeah I've definitely been there. Spent a good hour once chasing a ghost in a Cessna 421 only to find it was just grumpy contacts. My trick is a little less elegant though, I just use my teeth to hold one probe while I jab the other around. Works great until you accidentally touch the resistor and get a little zap. Guess that's why they pay us the big bucks, right?

milarodriguez1mo ago

Hug that probe with your teeth too, @hugoj12, and I swear you get a sixth sense for when it's about to slip (learned that lesson the hard way myself). I upped my game by clipping a little alligator lead to the probe so I can clamp it on the contact and keep my mouth free. But here's the thing, if you're doing that resistor zap trick, you're already a step ahead of most because you've built up that muscle memory for where the hot spots are. Once you've tasted that 12 volt tingle a few times, you can almost hear when a connection is bad before you even touch it. It's like the plane talks to you through your fillings or something, you know?