Also search this site for opening the trunk on a R129 SL 90 - 02 . There was a way that you could use a metal rod fished through a license plate bolt hole to pop the latch.

Given S class parts are cheap, you could cut through the tail light for access. Don't randomly cut / break as you don't want to damage the body or trunk trim. Also be sure you don't turn on any lights until you have the tail light plug removed.