Just fixed the clock on my car thought this would be useful added here.
When I got the car the clock didn't work and I needed to replace the speedo cable so took the opportunity to have a look at it whilst doing this job. When I removed the instrument cluster ( round dials ) the clock wire ( purple I think ) was disconnected and insulated ( "...mmm" ). To remove the clock you need to remove the four large screws holding the perspex front cover in place. The clock is held in by two screws. These screws earth the clock via the circuit board; power to the clock coming from the aforementioned purple wire.
You need to remove the rear cover held on with three nuts, then carefully tease it off.
You can see the connection which has come adrift ( solder joint has fractured ) in the centre of the photo . To fix it hold the "arm" with tweezers whilst heating the solder with a soldering iron. When the solder melts position the arm back in place then remove the heat and hold steady until the solder solidifies.
The clock is a mechanical type but is "wound" every minute or so by a coil ( you can see it behind the broken contact in the photo) and a set of contacts ( not shown )one of which moves. When the contacts are closed the coil is energised, this forces the moving contact away from the fixed contact against a spring and a ratchet. The contact moving away also breaks the electrical circuit. As the clock runs down the moving contact moves back toward the fixed contact, approximately one minute later the contacts touch and the cycle starts again. I had mine connected to a bench power supply set to 12 volts to test it ( but you can use a battery ) connect +ve to the spade connector and -ve to the clock metal chassis; there is zero current taken for one minute until the clock is "wound" when you get a 1.5 amp spike of current which forces the contacts apart. You can hear this characteristic "winding" for a split second every minute or so.
I can only assume that at some point the contacts had welded causing the 1.5amp current to be pulled all the time which would probably have flattened the battery on an infrequently used classic. I prised the contacts open with a pair of tweezers and dressed the contacts with a flat needle file. I then tested it for an hour and it kept perfect time. Refit the cover, job done.
You might be wondering why the clock works like this. Mains electric clocks use the mains frequency as a time reference so this is no use on battery powered equipment, I think also quartz clocks didn't become common ( read cheap ) until the late 70's early 1980's.
