I finally got a stubborn old autopilot to talk to the test set

Was working on a King KAP 150 from a '90s Cessna that kept failing its BIT. The manual said to check a specific pin voltage at the main connector, but the reading was all over the place. Out of frustration, I cleaned the connector pins with a fiberglass pen instead of contact cleaner, then put a tiny bit of dielectric grease on them before re-seating it. The voltage stabilized and the unit passed on the next try. Has anyone else found that old connectors just need a different kind of clean?

3 comments

3 Comments

jamienguyen1mo ago

Oh man, tell me about it. Sometimes that old gear just needs you to get a little rough with it.

mark_cooper1mo ago

Honestly, is a fiberglass pen that different from contact cleaner? Both are just cleaning off the gunk. Maybe the grease did the real work by keeping moisture out after the fact. Seems like a standard fix for old, cruddy contacts to me.

veramiller17d ago

You said "the grease did the real work by keeping moisture out after the fact" and that actually makes me wonder if people are missing the bigger picture here. Fiberglass pens are way more abrasive than contact cleaner, so they can actually scrape off the protective plating on those old contacts if you're not careful. That's why I think the real fix isn't the pen or the cleaner, it's the fact that you're physically removing the oxidized layer that builds up over decades. The grease probably just saved you from having to do the same job again in six months. So honestly, it's less about which tool works better and more about understanding that old gear needs a different kind of maintenance than modern stuff.