Installing after market air horns

I have an air horn like you get at Harbor Freight that I want to put on my 2015 Tacoma to replace the OEM horns. Looks like I'll have to use the relay that came with it. I usually have done stuff like this myself and would like to again (I'm getting quotes of about $200 for someone else to do it which seems just crazy to me). Should be pretty straightforward or so it would seem. The only thing that stops me from jumping right in and doing it is that my truck has two horns and thus two sets of wires powering them. I need some help figuring out how to wire this thing!

Thanks.

Gary

 

pick one. both are powered when the wheel horn is hit (probably the same wire split to go to the 2 horns). have one of them trigger the relay and tape the other one up so it doesnt short.