I get this question several times a week. Though I talk about what it is I do to start a driving pony here, I realized, I haven't addressed this question in a simple way...
What would I start with when starting a driving pony?
A halter and two long lead ropes.
That's it. Keep it simple. A flat nylon or beta halter, with two 10-12' lead ropes.
Why do I do this?
I want my ponies to have a very clear understanding of what it is I am asking them to do as we start. Using a bit complicates things. It is also a great way to make them worried about the bit because the longer lines, the juggling of them, moving your hands on them, having them sometimes step on them, are ways to actually hurt their mouth. Using a halter protects that delicate mouth.
I believe we should all be VERY good at handling our lines. Using a halter and two lead ropes means I have to learn to juggle all that line, keep them tidy and pay attention so he doesn't step on them. It also means that sometimes he will step on them and will learn everything is fine if he does.
My ponies are 100% okay with having the ropes all around their legs and under their feet. If they are grazing online, step on the lead rope, up by the snap, then feel the pull if they try to lift their head, they will calmly lower their head, move their foot and then lift their head. No panicked jerking or fighting the pressure. NONE. This is an extremely important lesson for them to learn.
When we are out walking I watch both Oliver and Zorro lower their head, step OVER their lead rope, walk a little further down the road with the lead rope between their front legs, then lower their head and step back over the lead rope, so it's no longer between their legs. Pretty smart right? I don't always try to fix things for them as I understand problem solving only helps them be responsive and not reactive later on.
Sometimes, they will step over the rope and then hop along on three legs. They have learned to simply come over to me and I will fix things for them. There is NO panicking when this happens. I would say 75% of the time they just fix the issue themselves.
Do I need a surcingle?
No. I don't suggest getting a surcingle or a long lining/training/biting rig, unless you are doing a lot of pony training for the show ring or doing in hand dressage. The long lining kit/biting rig/surcingle is a saddle with rings to run the lines through. It does not have shaft loops. Nor is there any way to attach shaft loops. It also does not come with a breast collar of any kind. So this set up can NOT be used for pulling. And shouldn't be rigged for that!!!!
What WOULD I buy?
I would eventually purchase the driving harness you want or need for the type of driving you will be doing. This will come with the saddle and shaft loops and a breast collar, all things you'll need to graduate to the travois step of driving training.
When should I purchase the harness?
This can wait for a little bit if money is an issue. I typically walk several HUNDRED miles behind my ponies with the halter and the lead ropes before I ever put any harness on. I do sometimes put harness on to make a video, to loosely fit it to the pony, etc. But I don't work them in the harness for some time.
If your pony is young, I would wait until they are at least 3 years old to purchase the harness. You still may need to switch parts out as they finish maturing, muscle up and change shape. But you are more likely to be near their grown size if you wait until they are three.
I bought Zorro a harness when he was a 2 year old and he pretty much out grew it by the time he was 5 years old.
I have a harness for Oliver, who just turned 2, but am prepared to swap out parts as he finishes maturing. I did this because I make videos and write blogs and often need photos of harnesses and harness parts on my ponies. This time I want to be paying better attention to the parts Oliver outgrows. He will NOT wear the harness for ground driving at all this year. Just for videos and photos!
So what do you need to start training your driving pony?
A halter and two long (10-12 foot long) lead ropes!