I had a similar problem. water was spilled on a MacBook Air (2015 I think), after drying for a few days, it turned back on, but the keyboard and trackpad were not working properly. They were working, just intermittently. I took the laptop apart, and removed the trackpad cable. There was a small amount of corrosion on one end of the connectors. Using some alcohol and a Qtip, I was able to clean it up. Reassembled and it works great!