I presume you never hooked up the (originally planned) aux lights via the ground trigger circuit?
You would use the ground trigger (blue) wire connected to the horn signal and the output channel directly to the horn, no relay required.
You have to use circuit 5 (brown channel) - it is the only one that goes over 15A
And you need to make that one, the Ignition AND Ground Trigger while stting circuit 4 back to ignition only.
You can only have max of 60A total, so whatever you add to circuit 5, you need to deduct from another channel - if disconnecting the OEM horn, you can reduce circuit 1 significantly - 7A should be good for that after you take the OEM horn out.