Just recently, my 89 300E failed to start after driving for several miles. The air conditioning was on, and I noticed at stop light that the air seemed to slow in it's power----well when i cut car off at the office it would not start. I jumped it, and it started immediately. Took to service center----and belt was loose----mechanic stated the belt tensioner needed replacement---did so----however today--just one week later cut car off---and would not start again---would not turnover----jumped it started right up-----Any suggestions what this might be---just invested 569.00 for prior repair and it seems problem persists.

Have someone check the alternator & battery
you may need a new alternator (rebuilt is available from Bosch)check the charging first
loosed belt could cause low charging too!

Another thing that I have seen is the brushes in the back of the alternator/external voltage regulator assy. When the brushes fail, there is no warning as to when the battery will die ( the warning light on the dash will not come on because it goes through the regulator to illuminate) Just have the regulator replaced if it is faulty. It takes about 20 min to do.

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
LEAD TECHNICIAN FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM