I pulled my cluster out of the dash to fix my fuel gauge. The cluster is supposed to be grounded through the screws that hold it to the frame, however after years of leaky wiper seals and everything else, it wasn't properly grounded anymore.
I ran a separate ground lead back there, and made it long enough so I could easily pull the cluster with it attached.
I used a ring type Stakon on each end, and screwed one end to the dash frame with a self tapping screw, and the other end went to one of the screws on the back of the cluster which hold the printed circuit board to the cluster - that's a grounding screw as well as a mounting screw.
Not only did my fuel gauge start working, but all my dash lights worked for the first time in 10 years as well.
As for wiring, you can buy the kits and struggle through them, or you can just buy a used harness which is much less confusing, and cheaper.
I've got a 69 Dart 4 door parts car with a good uncut dash harness if you need.