There is a turnbuckle adjuster with a jam nut on the cable accessible through the back panel's access hole for the seat belt. You can get your figures through it to adjust the the cable, but it is tight. You must slacken off the jam nut, 11mm if I remember correctly, to then be able to turn the turnbuckle adjuster (it is faceted and is 8 or 9mm). I was able to get mine adjusted. I believe you can also get to the cable via the spare tire hole but I think the adjustment is more difficult or impossible that way. Hence I went from the inside.
Cheers,
