So when i got the bike it had no horn.

Assuming i buy the horn itself of ebay, what do i need to do to wire it up?

Should I not even bother and get a louder horn since the stocker is dinky?

Get the louder one. I have the Nautilus under the seat where the stock airbox was and it is great -  loud as hell.

I have the nautilus in the stock spot. Check this thread out for more info

http://gstwins.com/gsboard/index.php?topic=43296.0

This is the one I went with. I think $17 including tax. Pretty Loud.

I put on the Hella rally horn in the Wiki. It's a lot louder than stock. I love Fiamm horns too.

I was on a city street a couple days ago waiting at a light, and it was dusk, and I heard a freakin' TRAIN just down the road! We have NO trains nearby! Then I see a big Ram truck or something coming down the street and I hear the freakin' train but CLOSER! He had a set of locomotive air horns set up on that baby and was scaring the bejeezus out of people left and right! I loved it, I have always wanted a set myself for the freeways around here.