There is VECU located in cab. It is Vehicle control unit. It is the same like in Volvo and Renault trucks. All driving control switches and gas pedal are connectred to VECU. It is in dash (three connectors green, small green and blue). VECU controls engine ECM mounted on engine via J1939 (+1708 as redundancy). LCM/Flasher is light control unit. It is in cab too.
Brake control unit may be frame mounted ore cab mounted.
BBM is used only for auxilarry equipment, it is installed it is not in the same box with VECU like with volvo. on Mack and Renault trucks it is in other box, really looks like VECU.
If you have 2012 mack you most likely have a mp8 engine and the ecm is on the driver side of the engine and it is painted the same color , it will have to large plugs thet unlock sideways, cant miss it, it is about 12" by 12" I dont think adding a ground will help but good luck