start no start

working on a friends 74 duster and had a crank then no crank problem. then cranking stopped so I traced it to no power to relay in crank position. after follow the wire back through the harness found a module that had power from start position but no power out to starter relay. I`ve never seen one of these boxes, it has a circuit board in it, search online said it a safety seat belt disconnect??? any help please.