See my post #10: http://www.peachparts.com/shopforum/showthread.php?t=116557

Check the negative battery cable where it connects to the chassis under the rear passenger seat. It may look good at first glance, but remove the connecting nut and inspect underneath; you may be surprised at what you find.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280