Okay, everyone wants to use a Scotch Lock to tee into a wire. DON'T. Especially on a motorcycle that sees more vibrations and exposure than a car or something. They cut wires, get corroded, come apart and otherwise fail at the worst possible times.
I have been meaning to do this post for a while, but the opportunity came up and I had to do the job and take pictures on the fly as best as possible. I needed to tee into the blue high beam and green ground on the GI Joe Desert Action Cycle for running lights.
First off, strip a bare spot in the middle of the wire to be tapped.
Spread the bare wire open.
Rosin the stripped end of the wire that you want to use for your new accessory or whatever.
Poke the new wire end into the hole of the stripped wire. Twist the new wire(s) around the stripped part of the old wire. Use an alligator clip to hold everything together.
Solder the connection. Let it cool and give a tug to double check it.
It's hard to see the picture, but use a zip tie to hold everything together permanently. That will keep the wire from pulling out too easily.
Ideally you can slide a piece of shrink wrap over the joint, but otherwise electrical tape or liquid electrical tape can re-insulate the bare wires.