As you probably know, I drive an older car. Old enough, in fact, that it has a few mildly intractable problems, such as the fuel gauge, which only works intermittently. It's seemingly random, but today I finally figured out the pattern. It had seemed to correlate with cabin temperature, but not during summer; when it was warm in spring, the gauge would work, but for summer it wouldn't. This puzzled me until I finally figured out the human factor.
You see, my car has working air conditioning. This pushes cold air through the ventilation ducts. The fuel gauge is on the extreme left of the instrument cluster, right next to the vent duct leading to the outermost vent on that side.
So, I have a dodgy connection somewhere in there, which sometimes expands enough from heat to make a good connection, and can be cooled to the point of not making the connection by the air conditioning cooling the ventilation ductwork. I'm inordinately satisfied with myself for figuring that one out.