The clock is pretty much the same as most mechanical clocks except it has an electromagnetic solenoid that rewinds the clock spring every minute or so. When the springs winds down, a set of contacts are closed and 12 volts energises the coils which kick a ratchet mechanism to wind the spring and separate the contacts. This design uses much less power than a motorized one would.
1) Remove instrument panel cover - 4 screws
2) Remove one phillips head screw holding clock in it's lower left.
3) Slide clock over to the left and out towards you.
4) Disconnect orange power wire. Remove clock.
5) Place test light clamp on metal clock mounting plate and tip on power wire. If good proceed to step 6. If no power is present, check fuse and to see if black ground wire is hooked to clock mounting plate. It's on the backside and hard to get at. The dash is plastic so it needs this.
6) Chances are that the 40 year old mechanism has dried out and just needs oiling!
7) Bend the 4 tabs up straight, that hold the rear cover on, and remove it.
8. Use a pin oiler and lubricate all the mechanism pivot points.
9) Hook up 12 volts and you should hear a click from rewinding the mechanism if it isn't ticking already.
10) If it still doesn't work, check the contact in the center for carbon buildup. Also check continuity thru solenoid coils. ~40 ohms
11) The tabs are hard to bend so I just used hot glue to hold the rear cover back on.
There is a slider adjustment screw that changes tension on the govenor spring that would affect clock accuracy. When I figure which way is what, I'll update this thread.
Both clocks I checked started working with lubrication. xD