I have 1993 300SE. At the beginning the ABS light illuminated a couple of minutes after starting engine, then no speedometer and heavy steering. It went off after cycling the ignition,did like this 3 or 4 times and now is on all the time. I checked front left ABS sensor, it shows about 1000 Ohms resistance and generating voltage when I spin the rotor. Sensor wiring checked OK. Both front ABS sensors cleaned. There is a strange thing: no way to retrieve fault codes from the ABS module with LED-and-button tester. When I connect the testing wire to the pin #6 of 38-pin socket(ignition on of course), it's glowing the dim light and no codes whatsoever, no matter how I push the button. Another strange thing: base module (pin# 8)consistently gives fault code 12, which means blown F1 fuse, BUT the F1 fuse is OK and there is a steady onboard voltage on both sides of the fuse. By the way the voltage is 12.92 ignition on and 14 volts engine running. I changed ABS module with another one from a reputable junk yard, no changes, ABS light still on. Please, help

Sounds like the base module isn't supplying power to the ABS module.

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Does the ABS function?

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Indeed. There is a voltage on the fuse F1, but no voltage on the pin 8 of the base module, which is supplying power to the ABS module. There is a relais between the fuse and pin 8 which(relais) for some reason is not functioning. Should I replace the base module altogether or can I bypass this relais and connect the fuse to the pin 8 directly? Thanks a lot for your priceless help.

I don't think it can function without power