Electrical help needed

So I'm cleaning up some of my wires and I have a thick red wire that has been cut. It's a battery pos wire and i found where it came from but how do I know what circuit number 142 is? Is there a website or something that explains what circuit numbers are for my 01 GMC?

I punched circuit 142 GMC Sierra into Google and found that it is "Brake controller 12 volt source" for the tow package. http://www.gmupfitter.com/publicat/bull/bull57.pdf

I found it on there.