2014 with 1998 Detroit 60 swap.

My father in law owns a trucking company and he loves to swap Detroit 60s into all his trucks. I know mechanics but never one a big rig. He doesn’t know computers so here I am to help him. The swap went smooth (2014 Freightliner got a 1998 12.7 Detroit 60) and everything works how it should except the gauges, they will sweep and light up when ignition is turned on but not a single one actually has any readings after that. Using ECM and conversion wiring harness from KustomTruck out of Oregon. Any ideas or help would be great. My short reading and google has me thinking it’s something to do with the J1939 but idk!