Let me restate things, for my own clarity.
Building this harness, I have the original engine side plugs and wires that came with my pathy. The 76M connector has 4 wires. Two for the speedo (Red & White), and two for the neutral and 4x4 transfer switches. (Yellow/Black & White/Black). There is no green wire running to the connector, but both of my AT switches have a green wire coming from them.
I have a 78M (The MT's version of the 76M) from a 94 stick shift pathy, and all the drive train plugs it ran to. IE the MT neutral switch, reverse lights, speedo, and the two transfer switches. The single wire transfer case switches here use the same Yellow/Black and White/Black combination.
I also have the 76M connector from a 92, AT pathy. It had the Yellow/Black, White/Black, and green Wires. Here the green wire ran back up to the engine bay and into the harness through the 76M connector. So at some point after the changes made for the 94 model year, they ran the green wire elsewhere.
At this point I'm with you in thinking the green wire is a ground for the switches, but I'm still wondering where it went. (NEVER clean the garage while a project is underway, I'm telling ya) I'm half tempted to ground it out to a nearby frame point, but want to do more research first.