VSS = Vehicle Speed Sensor, used on the later trucks with electronic speedometers. I think the '89 is mechanical.

There must be a connection for the reverse light switch in the transmission. That is where "reverse gear" lives, so that is where the swicth must be. Maybe someone has cut the wires off the switch, but look for something screwed into the side of the transmission that is not a bolt and that is likely the reverse light switch. Same on the t-case, that is where "4WD" lives so that is where the 4WD switch is. It is usually up high near where the shifter is attached. On my '85 is it on the passenger side, on a '94 pickup I worked on it is on the passenger side, both 22RE, both 5-speeds, so I would guess yours in there, too. Those two switches connector to a short wiring harness that runs from the passenger side of the engine bay, up and over the engine to pick up the two switches.