Make sure when you hook up orange/black that you also enable option 14 in the remote starter so that it activates the alarm inside the module. Also, by default it will only honk on the 2nd lock press from the RF kit. If you want it to honk with each press you need to change option 11. All remote starter options are displayed in the quick guide (https://fortin.ca/download/33021/rf642w-install-guide-33021.pdf)
If you ground the horn yourself does it beep?
What RF kit are you using with the evo-one?
If you wanted to use the factory horn this is the vehicle information I have, be sure to test before connecting:
Driver kick panel, junction connector
18-Pin white connector