Please help with electrical prob on 50 yamaha

[tg9r]

Power trim switch on throttle started blowing main fuse when going up. Have narrowed problem to throttle control. Trim always worked fine using switch on motor, and now it works fine now that I have disconnected a black wire that was connected to the light blue wires that activate the up direction. It now works on the motor and throttle without blowing the main fuse. This black wire goes to both the ignition switch and kill switch. Can I conclude a problem/short in one of these switches because the motor cranks even with this black wire disconnected? Also, any sure way to check these switches before I just start changing? Also, any idea exactly what is this black wire for?
Sorry for the long post but any help would be appreciated.