@raftor01
Sorry to bombard you with all these questions but I'm having some trouble figuring out how to use the harness. How did you connect the two pin looking end pieces to the stock horn connector? The ijdmtoy diagram says those two are for the horn connector.
And in the other picture, did you use the black box at all? There's no mention of what purpose it serves. Also, is that metal ring on the red wire is supposed to go under the bolt on the battery?
The stock horn is grounded through the bolt that attaches it to the engine bay. That's probably the other wire you're looking for. The new horns (assuming you got the same horns as I did) each need a positive and negative lead (from the harness). The remaining two (positive and negative) wires are the trigger. The positive end connects to the positive end that the stock horn connected to. The negative end connects to the negative terminal of the battery.
I'm not sure what "black box" you're referring to other than the relay that is included in the horn package. I did not end up using that at all.
That bolt on the positive (and negative) of the battery is for attaching accessories to the battery. So, yes. The ring goes under the bolt.
Honestly, I'd advise that you turn to someone (a friend or professional) who can see how this system works and explain it to you better than I can.
What I can tell you is that the existing wire that triggers the stock horn becomes the trigger for the horns hooked up to the harness. This entire system is connected directly to the battery. It's difficult for me to explain in further detail than this.
I hope you're eventually successful with it.