A quick write up on what I did, and thoughts on what I might do different next time.
I started with purchasing the Motohorn 3.0 direct drive compressor kit. Comes with trumpet in either chrome or black. It includes a mounting bracket that I didn't use, and 2 lengths of wire far too short for my needs. A couple days after ordering, I got an email offering a huge discount on a second horn, so before even testing the first I had the second on order.
Initial thought was to go behind grill, but with the active shutters etc. it didn't seem like a clean look. I decided on directly behind the front bumper, and used 2 existing bolts on either side to mount my plate. The bolts hold the bumper mounting brackets.
I'm not a metal worker, but I'm stupid enough to think I can do anything, so I ordered a couple 16ga aluminum sheets from my local metal place. 16ga is just about 1/16 inch. I had the 2 pieces cut 6" x 24". I ordered 2 because I fully expected to screw the first piece up. I had wanted 5052, as its easy to machine, and is also easy to form, but what they had available for same day pickup was 6061. Turned out just fine, but I was afraid the 6061 would crack or split when formed, and I didn't feel up to annealing. I had never made speed holes, but I am YT certified, and I had seen that some people got positive results with 3D printed dimple dies, so I printed one with ABS plastic and 100% infill. I used my woodworking forstner bit to drill the speed holes, with the drill press belts set to the slowest possible setting. Put the dimple dies through the holes with a bolt through the middle, large washers on either end, and used an impact to crush them together, formed all 12 holes with no cracking.
totally unnecessary scope creep: I had a bag of Hemi orange powder coat, a cheap harbor freight powder gun, and my old electric smoker converted to a powder coat oven. damn fine results.
I didn't like how the compressors were designed to mount from a single bolt near the end, so I printed a couple ABS clamps/supports that allowed for them to mount with 2 bolts, and now no bouncing around.


So next was the wiring. I used 12g primary and ran 2 red 2 black along the existing harness to the firewall. In retrospect, I couldve grounded the compressors right near the mounts, and saved myself 16', but I had already run the 4 wires in loam.
Since I had the second sheet of aluminum, I did a little cardboard assisted design, and made the relay mounting bracket. Loosely copied from Outback Kitters' design they sell for the 5th gen trucks. It seems our cowl has a little kickout right where it slopes up, and bending the bracket along that path gave the panel a ton of rigidity. made L brackets, some riv nuts, and now a nice place to mount the Painless wiring I already had, and the relays that came with the horns. That side quest took another 5-6 hours, and my afternoon project is now stretching into its 3rd day.

I tapped in to the horn signal wire under the PDC, F42 I believe. I was afraid it would be one of the wires that are jam packed like sardines in one of the 4 cam lock wire bundles, but it luckily wasnt, and was very easy to splice in to. I ran that wire, and a return wire through the firewall, and up to the middle of dash.
I had a custom rocker switch made, and I am NOT going to name drop the company, because they ignored my instructions, and sent me a not quite what I wanted switch.
I have 2WD, so that means I had a poverty button right below the shifter, which made for an extremely convenient and easy to reach location for the switch.
It is wired so that when to the left, the normal whiney horn sounds, and when I need to get someone's attention, flip it to the right and all horns sound.
I also tapped in to the dimmer wire behind the light selector, and ran that over. Since the rocker has both dependent and independent lights, I meant for one to be on when in curtesy mode, and both lights when in Hey Get Out Of The Way mode. I realized that this wasn't well thought out, and so I may go back and address it later. As it is, one side lights up all that time, the other does nothing, although it might actually light up slightly when actively honking, I don't know I havent been staring at it when I tested the horn.
Maybe someone that knows electrics can help me sort the issue.
So, now for the good, and bad, and the ugly.
The horns have a great deep bass note, very fitting for our trucks. Since they are direct drive with no tank, they aren't nearly as loud as they were when I blew my garage compressor through one, and scared my neighbor.
Now that exact thing, the direct drive compressor: it takes a milisecond to build sufficient pressure to start the trumpet sound. I can hear my stock horn honk for just a fraction of a second before its big brother steps in.
I've talked with a cop friend, and demoed the horns. It was his opinion that unless I'm driving through a neighborhood blasting these in the middle of the night, they arent going to be obnoxious enough to get a ticket, they just sound right.
Had I experienced these before starting the project (who am i kidding, it was more like 4 projects) I wouldve had the horn signal wire go directly to 86 on the relay, and forgotten about the rocker, but this was planned out in my head, and once that train is rolling, there's no going back.
For anyone wanting to do something similar, I will share print files, or whatever I have. My way of giving back to a forum that has saved my bacon many a time.
TLDR: bumper mounting bolts from the frame horns left and right.