It took quite a bit of website and manual searching for me too. I have a 2005 Ranger. Julius is right, it is on the firewall, on the passenger side, just under the hood. It is part of the mass of wires going into the Powertrain Control Module about midway under the passenger side windshield wiper (PCM is about 5 inches long with bolt through the center).
The Haynes repair manual for the 1993 thru 2005 Ranger has an engine wiring diagram in the back (for 1995 & later) that shows a Gray/Black wire coming out of one side of the VSS and going into #58 on the PCM. It shows a Pnk/Orange wire coming out of the other side of the VSS and splitting with one leg going into #33 on the PCM and the other leg going to a ground symbol. (I thought wires with the black stripe went to ground).
I haven't installed my Z3 as I'm still in the process of figuring all this out. I don't know if I'm supposed to connect the Z3's VSS wire to the above mentioned Gray/Blk or to the Pnk/Orange. Also, don't know how I'll get through the firewall or if one of those VSS wires comes through under dash and I can connect there. Help would be appreciated.
Good luck.