I got an EPA noise notice last weekfor my pipes being too loud  and have an appointment to produce my bike for inspection tomorrow.  I was removing the V&H Big R's tonight with the intention of switching back to stock.  All was going well and i was undoing the oxygen sensor nut (rear one) when the other end came out without me seeing where it came from.  It is a two pronged male plug but I looked for about an hour trying to find the female end with no success (story of my life) I can see where the front one goes but I couldn't see a similar part in the middle of the bike or under the seat.  Anybody able to help with a description of what I should be looking for and where I find it.  I need to move quick.  My bike is a 2010 Wide Glide.

When you say "behind" the battery box, you mean towards the rear of the bike or towards the middle of the bike? Do I need to t ake the battery out to get at it?

Thanks guys.  I found it behind the battery got my stock pipes on and the noise wouldn't wake my nanna. EPA tester will have to be happy with that.