Sounds like it might be the kill switch or ignition switch, if you can see if you have voltage on the ignition switch side of the fuse you can eliminate the ignition switch. If one of the switches are bad you may be able to work them back and forth a couple of times to see if they will make contact. Been awhile since I have troubleshot a staring issue but checking these wont hurt.
I changed out the stock 150/80-16 tire for a 130/90-16 tire last tire change and it handles a little better at slower speeds but I think the 150 did just a little better at highway speeds. This tire has about 12K on it now, the difference to me was not enough to go out of may way to get one over the other.
Puc,
It is a piece of heavyduty heat shrink with a band of solder in the middle, slide the two wires into it till they overlap in the middle, heat with a heat gun or lighter untill the solder melts.