I have two questions regarding a 1991 F-250 that I recently acquired through a family estate distribution. First, after locking the front wheels, can I engage the four wheel drive option via the inside shifter while the truck is moving or do I need to be at a complete stop before engaging the 4WD option? Secondly, last week the tail lights worked, but all of a sudden they went out. However, when the truck is put in reverse, the taillights come back on. Any suggestions as to how to attack this problem? Thank you.
The hubs and transfer case are manual systems. So the vehicle must be stopped when shifting the transfer case into the mode you want.
As far as the tail lights, start looking for either a wiring harness problem or a bad ground for the rear lights.
I am going to direct you to http://www.ford-trucks.com , a site that specializes in these trucks. You may well be able to shift in to 4wd while moving, depending on what transfer case is in the truck.