For Drafting, you need a drafting harness, a sledding harness point of pull is too high for most carts/ wagons.
When you get your harness, let the dog see, smell, and get used to it before you put it on them. When putting the harness on or taking it off, make positive that your dogs leg folds up to their chest and that their paws, and claws (paying special attention to the dew claw) don’t get caught up in the harness. Take the harness by the section behind the neck in one hand, adding all the harness that rides on the top off the dogs back, and slide the harness over the dogs head. Next being very gentle with the dogs leg, fold it to the chest, as you pull the harness over the leg, repeat for other side.
pull the back of the harness down the back of the dog, and attach any other straps you may have (flap straps, breech straps) and giving a tug on the back of the pullpoints, pulling the harness tight to the dog.
Then, let the dog get used to just wearing the harness, and taking it on and off.
Do not put weight on the harness yet, just let them get used to wearing it.
After a while of that, add a string and a paper bag to the pullpoints. This is only to get the dog used to something following them. let them know its ok, and they are doing good only when ignoring the bag and/or walking forward and ignoring it.
when they get used to the bag being there, and completely ignore it, you can add a little weight to the bag, not much, just enough to let the dog know they are pulling something.
At this point, you have your dog pulling a dead drag, albeit a lite one. From this point you can use a 2×4 instead of the bag, or if you are starting in winter, use a chunk of carpet. Whichever way you go, the dead drag should not roll, or slide on its own, Be careful to make sure the dead drag (or anything else) never runs into the back of your dog, it could make them leery of pulling if they think they might be hurt.
This should be a week or 2 to do this much, taking a couple days at each stage, but don’t rush your dog, make sure they are comfortable with each step before moving to the next step.