240sxproject

I removed my gauge cluster with the digital speedo since my speedo only worked when it wanted to and my gauge lights never worked. Soooo my question is, which wires do i test? Should every connector on every plug be getting power to it? If not, (cause im assuming some are grounds), which ones should light up with my tester? I think my cluster is ok since it works sometimes but im not sure. It has no markings of it frying or anything. Please someone let me know...