sounds like the Park, neutral switch, located for an automatic on the Left hand side of the transaxle,, might just be dirty or one of the wires are loose.. on the standard the Ford service CD says its on the fly wheel housing..... same thing, wires should be checked first.. and the cd says a crowsfoot wrench on the automatic should be used to removed it...on the standard they show a plain old box end wrench doing the job....
get someone back there and look at the back up lights and go though the motions of shifting and get them to see if the light comes on at all just for a little while.....
