Just got a 1989 Santana 2500D and I’m also having trouble getting the 2H gearing to work. Did you ever get this sorted? A couple of times I got it to work for a moment, then it disengaged again. Driving in 4H in the meantime.
Just got a 1989 Santana 2500D. If I understand the manuals, your pink diagram would have 4L at the top left, 4H at the bottom left, and 2H on the bottom right.
I’m having trouble getting 2H to engage, so I’ve driven so far in 4H and 4L.