September 1987 on, the passenger's airbags were added as extra-cost option for the 1988 model year. The consumers could choose either driver's airbag only or driver's and passenger's airbags. For the US market, the driver's airbags were standard from 1987 onward due to the federal regulations; the passenger's airbags were extra cost option until 1989 when they became standard for models with V8 engines only and 1991 for the rest of model range. Traction control system (TCS), also known as Acceleration Slip Regulation (ASR), to prevent wheelspin (a Mercedes-Benz first). This feature was available on European models only from 1989 and 1991 and on North American models (560 SEL and 560 SEC) for 1991 only. A third brake lamp in the centre of rear windscreen was federally mandated in the United States from 1986 model year on. In some markets, it was offered as standard or extra-cost option. Comfort and convenience Courtesy lights on the underside of the doors, to enable the occupant to see the ground when exiting the vehicle at night. Rear reading lamps were fitted to the C-pillar enabling rear passengers to read or work at night without distracting the driver. Extra cost options for the rear seat passengers were: individually adjusted seat heaters (never offered in coupé models during its entire production run); bench seat that can move forward and back electrically by 10 cm (long wheelbase models only); foot rests; from 1987 on, rear windscreen window shades that are electrically raised and lowered by switch on centre console; and the back of front seats are contoured as to give more legroom. From 1979 to 1984, the driver and front passenger seat heaters were separate extra-cost options. From 1985 to 1991, both driver and front passenger seat heaters were offered as a single extra-cost option. Beginning with 1985 model year, the rear individual seats and centre console as appeared in coupé model could be fitted to the long wheelbase models if the owner desires, giving the car a 2+2 seating format. The individual seat is electrically adjustable by moving forward and back only. An optional fully automatic climate control system that used an interior temperature sensor to more accurately climatise the cabin. This sensor was mounted overhead (near the sunroof switch) so that when the roof was open, the sensor would detect cool air-flow and call upon the system to adjust heat flow accordingly. Exterior temperature