What is this and should the yellow wire be soldered to it?

Any ideas on preventing the wire from detaching again?

small cylinder with black knob on top attached to firewall to left of battery

I checked the C150 parts manual but didn't see it. Is there somewhere else I should be looking, or did I just miss it?

  • 2
    $\begingroup$ Are you working on this airplane yourself? If so you need to be aware of your local regulations. $\endgroup$
    – GdD
    Feb 18, 2019 at 15:35
  • $\begingroup$ Whats under door #1? that looks like it could be a cable connection cap, could be an antenna connector. Showing us whats under the cap could be of big help. $\endgroup$
    – Dave
    Feb 18, 2019 at 15:45
  • 2
    $\begingroup$ @GdD: I'm not modifying anything without supervision from an A&P, I'm just curious about what goes on with my plane and prefer to post here where the answers can potentially help others. $\endgroup$
    – Zaz
    Feb 18, 2019 at 21:01
  • 1
    $\begingroup$ @Zaz: Freehand red circle might be usefull to save time getting what you mean. :P $\endgroup$
    – Zaibis
    Feb 19, 2019 at 5:15

1 Answer 1


That is a fuseholder for the optional clock or optional Hobbs meter. The yellow wire probably should be connected to it but you should have a certified mechanic inspect it.

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  • 2
    $\begingroup$ Interesting to see the free wire maybe the one directly and permanently connected to the battery anode. $\endgroup$
    – mins
    Feb 18, 2019 at 17:00
  • $\begingroup$ Thank you! Where did you find this? I couldn't find it in the 1965 POH or parts manual. $\endgroup$
    – Zaz
    Feb 19, 2019 at 10:29
  • $\begingroup$ I recognised it as a fuseholder and had a hunch it would be for a Hobbs meter. I then did a Google search and found multiple references. $\endgroup$ Feb 19, 2019 at 14:22
  • $\begingroup$ Sorry to bother you, but I have a couple of questions: My plane has a wind-up clock and no Hobbs; also, there's no voltage between the wire and the cathode or anode. What does this mean? Could it be the generator fuse that is no longer used now the plane has an STC alternator? $\endgroup$
    – Zaz
    Mar 21, 2019 at 1:28

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