Join Date: Dec 2005
Location: Upper Central Midwest
Yes, you can just splice an extra horn in. I've been using is that way for over 6 years now.
I actually bought a "pair" of used GM horns and used the one that was the different horn note than what the Colorado has stock and spliced it in.
Just make sure you make good connections, weather tight. Soldering would be best or also buy another new connector what would connect to both horns. Sometimes in Ebay, you will find GM horns listed with the connectors still attached but cut off. Easy then to cut off the original and then splice in the other.
No new relay or fusing needed.