Please read the whole thing before attempting.. If you are uncertain, please ask! I don't want anyone melting thier harness!!!
Should be easy enough to do..
On a standard automotive relay you will have five terminals, labeled as follows:
85 - coil side 1
86 - coil side 2
87 - normally open
87a - normally closed
30 - common
Ok.. You must picture a relay as a remote mounted electronic switch. 30 is your common, in this case power feed to the lighting circuit would work here. You must font the wire that feeds power to the lighting and cut it. After it is cut, the end that still has power is your feed, which will go to your common, terminal 30. 87a is normally closed, meaning when the relay is in it's default state, it is connected to the common, terminal 30. You should connect the other end of the wire you just cut to 87a. Since this is normally closed, your lights should now work without any other wires connected.
Now for the coil. This is the actual "switch" portion of the relay.. It is basically a small electromagnet, and when you pass power through it, it will energize and move the internal switch. One end of the coil needs power, the other needs ground. Unlike the "load" portion of the relay, these are very low current, so you can use very small wires and a very light duty switch. The polarity of the coil does not matter, either side can be positive as long as the opposite side is ground. I like to make my switch ground triggered so there is no live power on my wires. To do this you need to connect one coil terminal to power. I would take 85 and connect it with 30, since in this situation 30 will have power when the bike is on. After that you will connect one end of your switch to ground, the other to terminal 86. The best way is some small black speaker wire. At one end connect the switch, at the other end you will ground one side and connect the other to your relay, this way you only have to run "one" wire to the switch since speaker cable has two conductors in there, and you can safely ground it inside somewhere near your relay.