I am installing a set of horns and want to put in a relay to go from factory horns to new horns with the flip of a switch. ? is where is the best place to find the main horn wire under the hood, and what color is it? Thanks in advance

The horns are behind the headlamp/marker lamps on each side. Removing those would probably be the quickest way to access them.

I am doing the same thing, going to use the disconnected pass side horn. If you are using air horns and powering a solenoid, I doubt you need a relay. I'm not planning one.

I am doing the same thing, going to use the disconnected pass side horn. If you are using air horns and powering a solenoid, I doubt you need a relay. I'm not planning one.
I am going to use a relay so I can switch between stock and air and still use the stearing wheel horn button

Can you do that? A great idea! Using a switch in the cab?

Can you do that? A great idea! Using a switch in the cab?yes you can with a relay that has both a #87 and a #87A terminal on it. so when the relay is off it will let the stock work and when the relay is on the air will work. I just need to find where the main wire going to both horns is and what color it is so I can put in the relay. there should be one wire going down to one horn and then a splice to go to the other one.

on edit: yes with a switch in the cab to turn on or off the relay

I believe the d side horn is the first in the chain. Remove the whell well shrouds to access them.

or go

HERE (http://www.gmupfitter.com/publicat/2004_BB/2003_Beyond_LD_Electric_CK.pdf)

and search the doc for "horn" and you'll find the wire color and conection.

or go

HERE (http://www.gmupfitter.com/publicat/2004_BB/2003_Beyond_LD_Electric_CK.pdf)

and search the doc for "horn" and you'll find the wire color and conection.
I could not find anything there

Why not? There's 38 occurences of "horn".

Looks like you could just tap the horn fuse at the underhood fuseblock, it is after the relay.http://service.gm.com/engif/000/000/832/832352.gif

Dunno why these schematics always come out so huge?

There's always somebody with "fish".

well thats what i did last night, I pulled the under hood fuse block apart and started testing and found the pair of dark green wires from the fuse going to the horns. cut it and put in the relay. works great, now all i have to do is mount the air horn.
Man I love this PLACE:ro)