Anyway, as I have previously stated, you must ensure that LFS has HORN1 currently active, so if you press your horn button, HORN1 sounds.
Also, you must have PGUP (Page Up) configured as your horn button for this to work too, otherwise you will just be clicking through the horns without any sound.
I have not tested this with any external programs such as TC Lights/LFS Cops etc, so no 100% that it will work seamlessly with it.
You say you haven't tried it with TC Lights, I haven't tried your profile yet, but I take it keeps the sirens on itself? So the one button will start the horn, cycle through and turn it off?
1st Button, on the G27 is the left middle button...
1st Press: Beeps HORN1, flicks to HORN5 and holds the horn down.
2nd Press: Beeps HORN1, flicks to HORN4 and holding the horn down.
3rd Press: Beeps HORN1, flicks to HORN1 and turns the siren off.
2nd Button, on the G27 is the left bottom button...
You must activate the siren first by pressing the left middle button to activate "1st Press: Beeps HORN1, flicks to HORN5 and holds the horn down"... Then, you may start to use the left bottom button to do the following....
1st Press: Beeps HORN1, flicks to HORN4 and holds the horn down.
2nd Press: Beeps HORN1, flicks to HORN3 and holds the horn down.
3rd Press: Beeps HORN1, flicks to HORN5 and holds the horn down.
Then it keeps looping. When you return to HORN5, you may press the left middle button twice to turn the sirens off.
The reason I made it so you need HORN1 as the starting sound, is so you can have another button mapped on the wheel as a normal "Horn" Or atleast thats what I use.