(this is too long to put in a comment)
The entire suspension isn't correct, which is mostly why the steering isn't working. You also made the hydros/steering deactivate after 40 kmh, which wouldn't be very helpful in a wagon. It would be better to use the option "i" (invisible), or no option. If you want to fix the steering and create a better suspension, you can use the docs
here, however I don't think they're the easiest to understand. To be completely honest, just took a double wishbone suspension from
here and modified it to work with my car. If you want, you can see how the different suspensions on that page work, and maybe take one (although you'll have to modify them quite a bit so they don't explode for some reason. Or you can just take the suspension from my car (yes I'm giving you permission to do so, no need to credit me) and tune it to your liking. I use Blender to do all this, but the basic tools needed (resize, move, rotate, add and delete vertices/nodes, etc.) should be pretty easy to learn, and makes suspension swapping easier. Also clean up the node coordinates please, these coordinates work but they're not very pretty: 0, 0.0015642929660898838, 0, -0.18325721970658146. And since your wagon is 4 tons, I highly recommend you to decrease the node weights withminimassand decrease the damping of all the beams to stop it from exploding, and decrease the spring of the wheels so they're a little more grippy