Google "Bay 13 + volvo", and enter Bay 13 web-site.
Go to the miscellaneous heading and click.
Go to "replace seat back cable" and click.
There is a two page article on how to remove the seat cover and
access the drive cable, motor, and worm gear assembly complete with
digital photo's.
Count on about 4 hours to complete the job and brush up on your profanity.

I just did this job last night and wish I could thank the author of Bay 13
personally - couldn't have done it without his site.
FYI, my cable was not broken, just needed lube on the drive motor side.
You'll need the following tools...
Cutting pliers to remove/cut 8 hog rings.
Phillips "stubby" screw driver. (for the worm gear housing)
8 mm box wrench - for the drive motor housing.
Needle nose pliers - to release the spring/clips.
8 cable ties - as replacements for the removed hog rings,
and a good light.
...and people laugh because I have a computer in my garage.
good luck,
Armie




--
Luck favours the prepared.