I think that is used to illuminate the icons on the front panel.
(someone one please correct me if I'm wrong)
If so, then the red wire need to be connect to a live that is only active once lights are turned on. The black wire just needs to be grounded.
Hope this helps!
PS: R/Y - Red With Yellow Tracker is the illumination wire, going by that diagram. This will be one of the wires on the back of the clock, if you need a place to piggyback from (you can use a power probe to double check)
