The clock in my 1967 Mercury has an interesting mechanism. It's a fully mechanical wound spring clock with a self-winding mechanism. When the spring unwinds it

The clock in my 1967 Mercury has an interesting mechanism. It's a fully mechanical wound spring clock with a self-winding mechanism. When the spring unwinds it closes a circuit on an electromagnet that quickly rewinds the clock spring. Every couple of hours or so you'll hear the click from it rewinding on its own. Unfortunately there's nothing to prevent it from running down the battery and they often need to be replaced due to burn out when the voltage gets low. Essentially the rewinder doesn't have enough voltage to actually wind the clock and the circuit stays closed.