Voltage gives an indication of life, but resistance is better to measure, and of course it's more work. Make sure you have all your wires labeled before you disconnect anything, although, you can just undo the molex connector to get access to the field wiring side, in order to measure resistances.
Since the controller is still keeping time, it isn't seeing any short circuits in the wiring, but an open circuit won't show itself on an old RC controller.