Hi people. im the proud owner of a 2006 mercedes cls 320cdi.  (wish i bloody wasn't).


Electrical issues need assistance.  What is the black 2 pin connector joined to positive cable on AUX battery terminal (new aux battery 5 days ago. Have nearly 13v engine off at terminals, but nothing at Aux battery relay?? still get convenience controls disabled message on screen, and car wont turn over? where does connector go? what does it do.


Hi there, 

Right now I have a 2007 R320 CDI that has a bad auxiliary battery. It starts right up and works perfectly. Except it shows the battery sign because the auxialry battery does not take a charge. All the accessories work just fine. 

I am saying these because you mentioned that the car does not start. A bad aux battery will not prevent the car from starting. 

Regarding the connector, I am not sure which one it is or where it goes. I will be trying to charge the old aux battery this week. When I do that I can take a picture for you.

Does the ignition turn? All dash lights on? Do you hear a click? Nothing at all? 

Test the relay, swap it or at least test it.

Are there any other codes? 

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