Side airbag sensors, location - GF91.60-P-4009-01B

Model 210 with code 290, 293, model 210  , from 6/98 to 6/99, model 210 as of 7/99, models 215, 220 

The side airbag sensors are located behind the cross member below the rear bench seat.

Illustrated on model 210: 

Fig 1: Identifying Side Airbag Sensors, Location

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.