cant find horn trigger on silverado

hi all- putting alarm in 2006 silverado. for the life of me, i cannot find the horn trigger wire. all diagrams say BLACK / YELLOW to black at steering column, OR BCM/gray plug/B9. can anyone tell me for sure where it is? and what polarity it is? if its negative then once i find it i should be able to ground that wire and honk the horn right? also, the install manual for alarm says this about horn: "Verification: This wire will register at positive voltage and register ground when the horn switch is pressed." i am confused by that statement. can someone explain it to me or is just a mistake on their part? thanks

i always grab it at the BCM under the steering column. there should be three plugs (if memory serves right) at the BCM: Brown, Gray, Blue. now that i think of it, there may be a small black harness too. at any rate. in the gray plug will be your horn. if you look close enough they even label the pins (row: a or b then position: 1, 2, 3, etc) it will be +12v at rest and go to ground when you honk the horn, therefore you can ground the horn wire and honk the horn

It's BLACK / YELLOW in the main harness from ign. switch. It goes down to a junction box right behind the knee buster.

thanks guys. that did it.