The W126's parking brake is a small drum brake on the inside of the disc. The rear calipers and pads have nothing to do with the parking brake system.

The parking brake pedal not coming up high enough to shut the light off is common. You should first remove the rear discs and make sure the shoes are in good shape. If they are then their is a spliter under the car right in front of the diff. This is used to adjust the cables and tighten the pedal up. Most of the time it is rusted up from lack of use. Cover it in wheel bearing grease once you free it up.

If your ABS light is on chances are its a bad ABS sensor, you can clean them when you do the brake job. If that doesn't do it they need to be replaced.

Now that you have an owners manual go to MB's website and buy a service CD.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200