So I bought a snapper 1 year ago. My dad took the battery out of it for the winter. However, I go to plug it back in for the spring when I realized there were 3 wires not pluged in. I followed the manual and attached the positive and negative, but I still don't know where this third black wire attaches. It seems too short to attach anywhere and I can see anywhere where it needs to be attached.

My question was: are there only 2 wires that attach to the battery, or does this third wire also attach to the negative as some sort of a grounder?

Hi,
It sounds likely that you are correct and that is a separate ground for the harness. For safety's sake though, I suggest you post the numbers from the model decals and from the Snapper model number tag (2 sets of numbers there.)
Peace,
Clarke