Sounds like everything is on the right track. We generally leave these wounds open if their is nothing vital in the area. THey can be closed but after you pay a couple hundred dollars to have it closed up and then about 3-5 days later the horse wrips it open, and the owners are normally mad. The yolk colored stuff that you are seeing is normal it is serum and other fluid. You will want to clean it 1-2 times a day. Wipe the area with a paper towel. Then use some betadine scrub (soap) to clean the area and get any dirt and fly eggs washed away. Then keep up with the triple antibiotic ointment. I would also get some Thuja (like swat but 10X better, have to get it from your vet) You can put this around the wound to keep the flies away (they hate the stuff). Then I would get a couple of cheap fly sheets (1-2). This way when one gets nasty you can swap them out while you clean the other. If you cant do the fly sheets then you can put the Thuja on the wound over the triple anti-oint. to keep the flies away. So you are doing right, as long as your horse doesn't start running fevers and becoming lethargic you should be fine. When wounds are left open they can take twice as long at minimum to heal.

Quick tip: Get yourself some 4x4 gauze pads and a container that they will fit into, then soak the gauze in the betadine scrub, make sure it soaks in all the way through, then put the lid on and you have ready made scrub pads that you can use and toss.

Hope this helps