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Shoutout to the old A&P who showed me the wiggle test on a cannon plug
Had a jet come in with an intermittent heading flag on the standby instrument that was driving me nuts for two days. I reseated the connector twice, rang out the pins with a meter, everything showed good continuity, so I was about to start pulling the unit and sending it to the back shop. An old A&P named Ray walked by, watched me for a minute, and said 'quit metering it, grab the wire bundle and wiggle it while I watch the flag.' Sure enough, the flag flickered right when I bent the harness about three inches behind the plug, and the meter sat there reading perfect the entire time because the break only opened under flex. Turned out a busted wire inside the bundle had a couple strands still touching, enough to pass a static check but not enough to hold under vibration. Ray said that trick has saved him from pulling more units than he can count, and now it's the first thing I do before I condemn anything with an intermittent fault. Anybody else got a go-to trick like that for chasing gremlins that only show up in the air?
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barbara_lane557h ago
The wiggle test works on more than just cannon plugs too. Had a fuel quantity gauge on a King Air that would drop to zero about 10 minutes into every flight, and on the ground it sat there fat and happy reading full all day long. Spent a week on it, pulled the sender, ohmed the harness, all clean. Finally a guy told me to climb up and yank on the wire run behind the panel while someone watched the gauge, and sure enough the needle twitched when I pulled it. Turned out a pin in a butt splice was crimped on the insulation instead of the wire, so it held fine sitting still but lost contact once the airframe started flexing. The trick is flexing the whole run, not just the connector, because the break can be three feet back in a clamp somewhere. Meter it all you want, a static check will lie to your face every time.
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