Service manuals typically give a pin-out for the factory cluster, so you know what each wire does. Though it's rarely as easy as just cut/splicing the wires. Tach signals aren't always the same, the resistance values used for temp/fuel gauges might be different (resulting in no, or inaccurate readings), speedometer signals are typically a plain square wave and fairly universal, but the calibration is most likely off so you'd need something like a speedo-healer to put it back right again.
The tach tends to be the tricky one. "Noisy" signals, different ignition setups, ect, often lead to a jumpy needle, or the tach reading 1/2 or double actual rpm. Aftermarket clusters allow a lot of these calibrations to be adjusted, but factory ones never do since they were only designed for that one bike.