You didn't ground the reverse wire, too, did you? If you did, that will keep it from starting/firing since the CDI won't allow the quad to start in reverse.
How did this problem come about? Did the problem start all at once? Were you getting spark by pulling the recoil starter, before grounding the neutral wire? Has the quad been sitting for any length of time?
Most 4-wheeler problems are caused by a loose nut connecting the handlebars and the seat!!
You only need two tools in life -- WD-40 and duct tape. If it doesn't move and should, use the WD-40. If it shouldn't move and does, use the duct tape.