Hello, I just purchased a 1999 New Holland 2120 that will not operate in forward or reverse. The loader works and has plenty of power. The power steering does not work. I did some research and read where a couple people had a diode go out in their control module. I checked this and that...
Which transmission does your 2120 have? The gear version or the HSS version?
Assuming that it is the HSS version:
If you mis-wired or left open the AC wire on the starter switch, then two of the fuses on the fuse box would not get power. One of these fuses feeds power to the HSS control module. It is the 10A fuse. I would check for power at the fuse box with the engine running and also check all the fuses. If the HSS control module does not have power then you can't go forward or reverse.
This is the one thing that I can think of that would be related to changing the starter switch. Everything else would be a coincidence and would be covered in the post above by @kirkawilson