I agree with the above. 4 wheeled vehicles and a horse pulling for the first time can = expensive & potentially harmful crash. Even with a 5th wheel for steering they’re generally not great for starting a horse. Generally speaking you want to put enough weight behind the horse to discourage a runaway but not so much that you discourage it from pulling altogether. A 4-wheel cart is usually too heavy for one human to move but fairly easy for a horse because there’s little drag resistance and no weight transfer from balancing it.
Sleds:
Pros - enough drag to prevent or diminish the severity of a runaway. (It’s not a coincidence that sleds are used for weight pulling competitions!) Cheap to build. Easy entry/exit for the driver in an emergency.
Cons - the noise of a sled dragging can spook the $&&)(:@'hh out of some horses.
Two other options to try would be a farm style forecart like Pioneer makes or using an old truck hood for a sled. Check out the forecarts. They’re a very different beast from a pleasure-style 2-wheeled vehicle like a Meadowbrook. Meadowbrooks are a death trap if you have a runaway. No brakes, too light to ride the horse, and the design necessitates having to jump over the wheel to bail out in an emergency. The farm forecarts are kind of like the tractor of a tractor trailer. They come equipped with brakes, you enter/exit by stepping up about a foot from the ground, and have a rear hitch to accommodate farm implements, hay wagons, etc. They’re great when you need to get a lot of weight behind a new horse or team for safety but aren’t sure how they’ll do with something dragging behind them. (We once hitched a Ford 450 behind one for a new team.)
The forecarts are infinitely versatile. I originally bought mine for a horse that had completly the opposite needs of a young, strong horse. My aged Percheron gelding loved to go out driving but had arthritis to the point that he needed something lightweight and with brakes so I could hold the cart back off him going downhill so the britching didn’t sweep him off his feet. It was light enough that I could juuuuuust move it myself over a short distance on flat ground if I needed to. I believe they also sell sled runners for them so you can convert them in the winter.
Otherwise, consider dropping a single tree to the hood off an old truck. I know people that move 100s of roundbales a winter with this setup. Be careful with pulling logs. If you ever have a runaway it’s not enough weight to slow the horse and it doesn’t have to be a huge log for you to be seriously injured or killed if it swings out and hits you. Most people who log with horses like to use a logging arch for added safety. (Pioneer sells these, too!)
Good luck and have fun!
