adding a relay to a new horn.
 

i just changed my horn again to a stebel nautilus (man, this horn is loud!), but i'm having a fluctuation on my electrical system (just a bit), i know that the stock horns have a relay, but can i add another one? would this solve the fluctuating problem? and how do i add the additional relay? and where does the horn button grounds to the positive or the negative? any help would be appreciated.. thanks!

guys??