Yep, its the #9 wire on your stereo loom.
Wire it to pin 14 in the original ford stereo plug or the corresponding wire in your loom adapter.
Unless you tap the wires coming from fuse 75 or 76 in the hidden fuse box for the side lights.
If you post a good picture of the loom adapter ( the loom that bridges between your stereo and the ford plug ) then I'll know for sure.