IISM Engine Brake Problems

[mayhem1]

2006 International 9900i ISM CM875 engine brake does not work. Insight sees the clutch switch, service brake, the switch to change from low to high. It says engine brake output circuit 1 & 2 inactive which I presume would only become active when brake is activated? What am I missing besides going into valve cover? It appears everything electrically is correct. Also customer said Engine Brake has never worked since he purchased truck used. Thanks