NexSysLink gauges gain power and signal through the Mercury Junction box and data harness. The only source of failures are the touch pad that controls the multi function window display. The tach itself feeds everything, and the 555 ECM on the engine sends signals in digital SmartCraft format to the tachometer. We think you have an issue in either the NexSys data harness, the engine data harness, the tachometer or the 3 button touch pad.