Mastercraft Xstar - instruments do not work

Hello,
my Xstar 2002 has all the instruments that do not work. The instruments have been tested singularly on another boat and they work perfectly. The Italian Mastercraft dealer has tried another electronic control unit and nothing changes. The existing control unit also works perfectly.
Has anyone got any idea of how to solve the problem. The Italian Mastercraft technician is going crazy in order to find a solution, but no way.
Any help would be greatly appreciated. Thanks