On a 1991 Ford Escort Wagon the automatic shoulder straps no longer automatically open and close what interlocks or sensors do you need check?

It depends on the seatbelt sensors, the begin and end of track sensors, the inertial cut off switch and some other things. In this case, the inertial switch had been tripped. It's found under an access hatch. The hatch can be accessed via the wagon end of the car. There is a small plastic access panel that can be removed from the plastic over the right rear wheel. Inside, you'll find a small red button in a black housing with wires attached. Press the button until it clicks.