The connector sticking out the side of the seatback is for the lumbar switch. The '96-00 Limiteds had the switch in that location. I'm guessing that there is not a single 4Runner in the world with that switch still intact, the tabs break off and the switch just hangs there, with the seatbelt catching on it occasionally. So some folks glue it to the seatback, while others take it off, like apparently was done on yours. Here is what it looked like on my '97:
The later, -01-02 Limiteds, had the switch smartly relocated to the lower plastic trim piece along the side of the lower seat cushion. I modified my '97 to that setup when redoing the upholstery recently. Here is what that looks like:
If you want to go that route, you'll need the '01-02 Limited trim piece for the bottom seat cushion, and an '01-02 Limited lumbar switch (it's different from the '96-00 switch). And you'll want to get the leather kit without the cutout for the switch in the seatback, though I think they all come without that cutout.
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1997 4Runner Limited 4WD E-Locker ~200k | Falken Wildpeak A/T3W 265/75/16 | Pro Comp 69 16x8 | OME 2906 | B&M 70264
Addicted Offroad Front Bumper | Spiker Engineering High-Lift Hood Struts and Ultragauge Mount