ok... the text that you entered in this post, please redo the first portion because I don't understand your description, the more detail you include, the better the chance we can help you figure it out, in other words tell the whole story. i'm a fairly simple individual,
i like great pictures and a good story.
whatever that cord is, someone made it to extend a harness connection, can you post up a good shot of the pins inside of the plug, that should help figure out just what it is that they were trying to extend. it looks like a loop back for an O2 harness, what doesn't make sense to me is why it would be under the dash, check that harness over good, see if it has any resistors (at least one) inline with the wiring.