Toyota has experienced many generational redesigns in its models over the years. In addition, a safety upgrade to the three-way-shoulder-and-waist-harness that we use today was introduced as the automaker's standard seat belt in the late 1970s. Depending on the year and model of your Toyota, the following instructions may be quite different. However, the understanding of the process should be quite similar.
Locate where the top shoulder harness retainer bolts to the upper interior panel. Some Toyotas may have an exposed bolt on the harness retainer, while others may have a plastic snap-on cover (usually the color of the interior) that needs to be pried off with a screwdriver to reveal the retaining bolt(s). Remove the cover, if applicable, and then remove the retaining bolt.
Locate the bottom anchor point of the shoulder harness. This can be the point at which the procedure becomes widely different for different Toyota models. Some may have harness anchors bolted on the floor of the interior, on the outside edge of the seat. Some may require interior door panels to be removed. Some may require the carpet to be lifted, which can be done by removing the bottom door jamb kick-plate and then lifting the carpet. Others may even require removing the seat to access the anchor retaining bolts beneath the seat on either side of the seatbelt connections. Refer to the repair manual for your specific model and year of Toyota to follow the correct procedure to remove the anchor of the shoulder harness. Once the base of the anchor is exposed, the retaining bolt(s) are quite visible and removal of them is the same as for the top of the harness. For some high-line models, such as Camrys, there may also be a wire connection to the anchor base of the harness for automatic retraction. These may have electrical button connectors or be hardwired directly to the retraction module. If necessary, disconnect or cut the wires, leaving enough room to rewire to the new harness anchor.
Locate frame bolts if either or both anchor points of the seatbelt are retained by a bolt from under the car. Remove the bolts by holding the bolt head with a hand wrench, and use the ratchet and socket to remove the retaining nut.
Locate the anchor on the inside of the seat. Again, this may require removing the four bolts holding the seat in place. Remove the seatbelt anchor retaining bolts and then lift the anchor upward from the floorboard slightly. Many seatbelt anchors on Toyotas will have an electrical wire connection to the instrument panel information center. This is what shuts off the seatbelt warning light on the dash when the clip of the seatbelt is placed into the anchor. Again, disconnect or cut and then strip the edge of the wire, leaving enough room to connect to the new seatbelt anchor.
Rewire the anchor electrical connections, using the electrical butt connectors if necessary. Strip the plastic covering from the wires by using a wire-cutter/stripper/crimper tool. Twist the exposed wire to prevent it from fraying, and then insert it into one side of the butt connector. Crimp the butt connector to retain the wire. Match the wire color connections.
Replace the anchor retaining bolts on both sides, and the frame bolts, if applicable. Tighten the bolts with a torque wrench and a socket according to the specifications listed in the Toyota manual specific to your model.
Replace the shoulder harness retainer assembly. Torque the bolt(s) according to the specifications. Replace the rest of the removed components -- door panel(s), seat(s), door jamb kick-plate(s) -- that were required to remove the seatbelt assembly. Lastly, test the operation of the seatbelt, making sure the dashboard indicator light and, if applicable, the automatic retraction module are working properly.
