that is not a stock wire, if you want to know what it does you'll have to do a little research (under your hood)
1. open up the loom and see what wire it goes to,
2. the connection inside the loom: Is the factory wire taped into, or cut and extended (replaced) with the solid yellow wire
its hard to tell in the pic. Is there one wire that exits the loom, then a couple of loops with a wire tap at the end?
more info is needed.