Does a 90 420sel have rear brake sensors
 

I just had new brakes and rotors put all the way around my 90 420sel. I thought my car had rear sensors that would light up a light on the dash when the pads needed to be replaced. The mechanic stated that my car did not have sensors on the back brakes. Could this be true? I thought all 420sel's had the sensors. Is it just an option? I am thinking my wife has sensors on her 89 300se on front and back. Can anyone help me get this straight?

The W126 sedans have pad sensors in front and ABS sensors front and rear.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

MB didn't put REAR brake wear sensors until 1991 (USA). And then only with optional traction systems!!

SO your 1990 car shouldn't have rear wear sensors.