Could be a ground issue. Just take a wire and ground the case. Test the power wire to make sure it's hot. Clocks aren't very dependable over time(pun). Usually it's dirty contacts in the clock. Quartz conversions are a fun 'do-it-yourself' project.
If your clock has the original innards and the '69's clocks are like the '68s, they really don't "run" off the battery power. They are "wound" by a solenoid every 30 or so seconds. That solenoid is not very robust. Over the years, I've had 3-4 burn out on my '68. I could always see when mine are burned out.