you are observing what the carraige manager sees.
i used to keep a complete card cage with me for these trucks... i threw it out last year i haven't seen one in over 5 years. it is fairly easy to swap cards out in these trucks and sometimes it is the only way to troubleshoot these however thoroughly checking basics first is always a must.
the interface card is what takes the steering tiller inputs and changes them for the steer logic. one thing for you, i might be wrong here but you might have to physically close the deadman switch while running test 018 i really can't remember but an easy thing for you to check and maybe refresh my memory.

also in test018 did you pass step 6?