I have this exact same problem, I have a 1998 Dodge ram 3500 with a 5.9 L Cummins diesel five-speed. Only the tack will work and no other gauges will work, also I have no voltage coming from my alternator. Could the lack of voltage from the alternator be triggering these gauges for not working. Have done the tests on the gauge and they all sweep. Seems like cluster is getting power and is working correctly however when running engine no gauges work.