The brake pad light will come on when the sensor is shorted. Check the pads to confirm. You have plenty of pad left, giving you time to get all the parts together. If you ignore the light, you will eventually burn thru the sensor and the light may go out. Next stop will be whats left of your brake pad against the rotor.

My 1991 300CE only has sensors on the front pads.

glenmore
1991 300CE
2000 C280
1990 LS400