To answer part of your question; the circuit board is just a way to run a signal to all the different connections behind the dash without individual wires doing the work. The plug next to the speedometer has all the wires running to that single plug that has to line up a certain way to match up with the bare copper on the circuit board. In a 69 car that I use to own, all I had to do to remove the cluster was to disconnect the plug and speedometer cable to free the unit.
As best as I can tell, yours appears to be maybe missing some of the copper conduit at least at one of your dash lights; if that is correct, then everything downstream of that will not work. If you are missing pieces of the copper, then I would think it would be very difficult to repair. Cleaning the exposed copper so as to make a better connection is easy, just do as Jerry suggested with a pencil eraser. It is probably also easy enough to repair any damage to the non conduction film that covers the copper wire.
Lee.
