have some info for the 4000 need your mail, not seen one for a while, if i remember one load wheel turns then next second wheel then drive and returns the other way round( front wheels must hit against large stopping blolts this prevents rams from fully reaching allowing pressure to activate other wheels) if front wheels are turning ok on demand check the proximity switches on drive wheel they should light up but do fail and still light have a look at the opposite one to the one that is activated, sometimes there is a spare sensor just below the steering wheel in cab all problems i used to have were sensors either broken or slipped in plastic clamp and sensing something else, test with spanner to light up