ahh...someone must have decided they didnt need the antenna.
to re-install the base, your going to have to pull the passenger side front tire off and remove (or at least peel back) the inner fender. look for a loose wire (its large and black...sorta resembles cable tv-type of coax) hanging down. if your lucky, the whole base is dangling inside the inner fender. if your not, then someone removed all the original wiring along with the base.
guess its about time to hit the junkyard to rob the antenna, base, and coax (wire) from another ranger.