Ok the light is comming on, which is on the dash, that means the brakes are getting low. Does it mean the front, rear, or does it come on when either gets low?

Its the front pads, the rears don't have sensors.

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"spreading a trail of obnoxious where ever we go"
1981 300sd w/ 341,500 miles

http://www.wecrash.com/pics/ddda_banner.gif

If it's the yellow light, it's the front brake pads or low brake fluid (Check the fluid first).
If it's the red light, the parking brakes (and/or cable) need adjustment to keep tension on the pb pedal.

Red light is both the parking brake and the low fluid indicator on mine. Yellow light is front pad indicator only. Check your manual to be sure, but I would think yours is the same.

Len
'83 240D 345,000 miles

I agree, that should be true for all W123s.

You can test the warning light by having someone press down on the black buttons on the fluid reservoir.

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1982 300CD Petrol/Black Leather

Can you tell me how to do this test and the expected results? My light has been on for months, but the car stops fine. It came on after I washed the engine compt, so I might have messed something up.
Thanks.

My "Red" brake light came on, it was because the parking brake pedal dropped about 1/2 inch, just enough to make the car Think that teh parking brake was applied. I stuck an old losing lottery ticket inbetween the PB and teh switch, turned the light off.

I had an intermittant yellow and red light in my 300SD. Fluid was fine, pad thickness was fine. Sensor was faulty...shorting out...esp when raining. I tried electrical tape but still happened. Sensors are ~$10 for 4 plus shipping.

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1983 300SD 307k miles
1993 Ford Escort Wagon 215k miles
1995 Isuzu P'up 214k miles