Crossed the jumper cables on 2004 CLK500. Replaced the battery that was fried. Key wouldn't turn. I started by unplugging the SRS under the pas senger seat. After plugging it back up key turned and engine cranked but all my electronics are not working. I've pulled every fuse in all 3 boxes 4 times. Have bought scanners , test light , multi meters and even a manual but am not getting anywhere. This is my first Mercedes but I have worked on my own vehicles my whole life. The electronics in this vehicle are beyond my pay scale. Watched tutorials studied the manual and need advice.

 

Oh dear, that has to be one of the worst things you can do to your car!!!

Start at the beginning...

Do you have electrical drawings for the car, mainly fuses? What manual do you have, as only real one is WIS.

New battery fitted?

What scanner do you have, and what is it displaying for current faults? can it find all the modules on the car? STAR SDS is the best one, but can be complex and expensive. You must get a Mercedes specific scanner, not cheap generic ODBII scanner.

Start with a list of modules your car has, and try accessing each one. WIS will tell you what you should have.