Got a 120-2 that does the same thing they all do. Intermittent so slow as to be unusable. Discovered a while back that if I jiggle the harness connector where it plugs in to the ECM it will be fine for a while. Sometimes I'd have to give an extra jiggle because the swing brake didn't release or it would go to full swash, but the sweet spot was always there. Now it's either full swash or no swash, the sweet spot is gone. Looking with a magnifying glass everything looks okay, pins in the ECM are all tight and no signs of heat. So, is there anything it can be except the harness itself? I suspect a wire is broken in the insulation, but If I put in a new harness and the problem is still there I might be really sad and frustrated, and I don't want to be really sad and frustrated. So can anybody think of anything else it could be that would be affected by the interruption of current from jiggling the harness?
Could be a wire in the harness or where the wire terminates into the plug... or.... might be a bad/fractured solder joint on the ECM side of the harness plug. Have you completely separated the wire loom going into the plug so all wires are accessible individually for a good length? sometimes it's just being able to move ONLY one wire at a time to identify the real issue. I have also seen corrosion get into ECM's (not a 120-2) and make them do funny things.
Ronsii, split the loom in half (side to side) but with 60-plus wires....... Did notice that if I roll up a pair of gloves and shove them in behind the harness to change the angle that it approaches the ECM it changes the swash angle.
I chased a similar harness issue on a machine a couple days ago. Everything looked ok but I could not get it to work. Turned out the pins in the plug at a module had spread over time and were making intermittent contact. Cheapest thing to do would be to re-pin the harness plug. If it doesn't fix the issue you'll only be out a couple bucks for pins, the crimp tool if you need it and an hour or 2 of your time.
I actually considered getting a bunch of female wire ends and eliminating the existing plug, but the pins in the ECM are very small and I couldn't find a correct size end. Something should be available, but I couldn't find it online and Radio Shack is no longer much use. Maybe somebody, somewhere has an old harness that I could cannibalize the plug and a foot or so of wiring from.
Sometimes there will be a company name on the plug body that can be used to track down replacement parts or pins. Have you tried industrial supply stores? What about the dealer? Sometimes they can get ahold of stuff like that.
Never considered the dealer.
I believe Hitachi did have a part number for a harness repair kit available a few years ago. Not sure what it contained though since the boss refused to order it.