Remove the bulbs and pop the light cluster assembly out. On a Benz or Volvo, there are little nuts accessible via the trunk or rear of wagon that let the whole light cluster drop out towards the rear of the car.

Then tote that poor l'il smokey dude over to your wife's sink. Best she not be there ...

Pour in a tablespoon or so of raw rice into each light reflector via the bulb hole. Add a few drops of dish detergent in each hole.

Then fill each up with very warm water and shake the whole mess around for about 10 minutes.

The hard rice kernels get into all the little darkened areas of your tail light lens and reflectors, removing the soot. Pour the mess out, rinse it with soft water a few times, then let it dry in a warm area overnight, and you have tail lights that look nearly as good as new.

Take a few minutes to be sure that the lens is still well glued to the reflector. In the case of Volvo and Benz, the lens assembly often separates from the reflectors. This makes the cleaning job easier. After cleaning, I glue it all back together with silicone seal or 3M adhesive trim glue.

__________________
Thx/Reno
An American in France
88 300TD 5spd Sportline (lowered factory susp) - totalled by a flying deer
89 Range Rover V8 - the 4wd beast
02 Toyota minivan
05 Peugeot Partner 4x4 Dangel
88 International Harvestor 633SA
--Gone but not forgotten:
1970 250/8 C (sold to buy 450 SLC)
1972 450 SLC (sold after battling wiring harness problems too long)
1971 300 SEL 6.3 (sold after destroying two *very* expensive rear LS diffs)
1986 560 SEL (now my little brother's pride and joy)