What is the small cylinder on the firewall to the left of the battery? What is this and should the yellow wire be soldered to it?

Any ideas on preventing the wire from detaching again?



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?
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.