If I remember correctly - I wired a compact nautilus into my last bike - and the horn was only interested in kicking out the decibels if the polarity was the right way round.
If you're connecting relay pins 85 and 86 directly to BOTH factory horn wires, (on one side only of course. tape up the other side) polarity is unimportant. You only have to make sure pin 30 goes to Batt pos., and pin 87 goes to + terminal of compressor. Neg compressor terminal goes directly to batt neg. DO NOT run the compressor neg directly to the horn switch! And DO NOT run it to the frame!!
I also just looked at their so called "plug 'n' play" harness. No wonder why it's only $29.99. You have to first assemble it, fuse holder is junk and not waterproof, and the rest looks like no larger than 14 gauge wire.
My harness uses 10 gauge wire in all high current places. 18 gauge is used for the relay trigger wires, and the whole thing comes COMPLETELY assembled and ready to literally "plug 'n' play.
They also don't mention the brand/quality of the relay they supply....or do they even supply it? Shown nowhere in the pic. I use quality (read expensive) Bosch relays. You get what you pay for.
My Nautilus harnesses are $48-$52 including priority mail shipping. Length determines price difference.
They are a completely different setup and wire size than the Blaster harnesses I also sell.
PS.....if anyone wishes to purchase a harness exactly like the one pictured on that website, I'd be delighted to make it for them for only $25 shipped! By the looks of it, it's about $4 in parts. I can make a bundle off this!! :lol: