Oddly enough, the 2002 and 2003 Ranger owners manuals have different instructions for manual SOTF between 2HI and 4HI.
The 2002 owners manual has 2 different speed limitations based on the ambient temperature:
Shifting from 2H (2WD high) to 4H (4WD high)
Move the transfer case lever to 4H
(4WD High) at a stop or any
forward speed up to 88 km/h
• At temperatures below 0°C
(32°F), shifts from 2H (2WD
High) to 4H (4WD High) should
not be performed above 72 km/h
Do not shift into 4H (4WD High) with the rear wheels slipping.
The 2003 manual transfer case is identical to 2002 but the 2003 O/M says:
Shifting between 2H (2WD high) and 4H (4WD high)
• Move the transfer case lever between 2H (2WD High) and 4H (4WD
High) at a stop or any forward speed.
Note: Do not perform this operation if the rear wheels are slipping.