will not shift into 4wd

First determine which 4WD setup you have.

View of the Borg-Warner model 13-54 with mechanical shift. Electronic shift and model 44-05 are similar

Transfer Case Identification

There are three transfer cases used on the Ranger, Explorer and Mountaineer. There are 2 versions of the Borg Warner 13-54 (mechanical shift and electronic shift), a Borg Warner 44-05 (Control Trac) and an All Wheel Drive (AWD) transfer case.

The Borg Warner 13-54, mechanical shift transfer case, is a 3-piece aluminum part time unit. It transfers power from the transmission to the rear axle and when actuated, also the front drive axle. The unit is lubricated by a positive displacement oil pump that channels oil flow through drilled holes in the rear output shaft. The pump turns with the rear output shaft and allows towing of the vehicle at maximum legal road speeds for extended distances without disconnecting the front and/or rear driveshaft.

Electronic Shift Transfer Case

The Borg Warner 13-54, electronic shift transfer case, transfers power from the transmission to the rear axle and also the front drive axle, when electronically actuated.

This system consists of a push button control, an electronic control module, an electric shift motor with an integral shift position sensor and a speed sensor.

The electric shift motor, mounted externally at the rear of the transfer case, drives a rotary helical cam. The cam moves the 2WD-4WD shift fork and 4H-4L reduction shift fork to the selected vehicle drive position. The system has no select-able Neutral (N) setting.

NOTE: The manufacturer recommends that the Borg Warner 13-54 transfer case equipped vehicles should not be operated in 4WD (whether HI or LOW) mode on dry pavement. Severe drive line torsional wind-up will occur, possibly damaging the drivetrain components.

The Borg Warner 44-05 transfer case operates in the same manner as the 13-54, except that it also houses a transfer case clutch. This clutch, which is controlled by the Generic Control Module (GEM), enables the vehicle to be driven in 4-wheel drive on dry pavement by cycling the clutch to compensate for different front and rear driveshaft speeds (as in turning). The system has a dealer install-able Neutral (N) position mode.

The All Wheel Drive (AWD) transfer case is a 2-piece aluminum, chain driven, viscous clutch type unit. The AWD transfer case is always active in 4-wheel drive, thus producing a full-time engagement. The viscous clutch automatically distributes power to both the front and rear wheels, depending on need.

4WD Circuit wiring diagram

(best viewed in Google Chrome)
1993-ford-ranger-transmissions-4wd-circuit-1-of-1