There is a manual on the yamaha site with the diagram in it, but hard to read maybe the PDF is better than the online one.
http://www.yamahagolfcar.com/partsan...rsmanuals.aspx
It could be for the oil light, or there are audio and headlight kits from yamaha but not knowing what the wire is for that diagram should tell. It may go through the 10A fuse in that case it would not be good for much current. Be very careful about using yamaha factory wiring for anything, and they usually do not ground the frame some have a ground fuse....but not sure on the Drive.