I had an intermittant ABS light coming on in my 88 300E and it turned out to be a bad battery. When the voltage drops below a certain point (10 volts I think) the ABS system is disabled as it could become un-reliable. try checking your battery voltage and charging system. Mine was a shorted cell and replacing the battery fixed the problem.

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Dave
88 300E 250K Sold
2000 C230K Totaled @104K
2003 ML320 156K Sold
2009 E350 4Matic Sport 46K Sold
2011 ML350 60K Sold
2014 GLK350 46k Sold
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2016 E550 Cabriolet 48K