No accessory power after engine start. Recent alternator/battery change

Question by Craig McConville posted 9 months 2 weeks ago in 2001-2007 (W203)

Hi all. I'm a recent purchaser of a 2003 Mercedes Benz C320. The vehicle had been sitting for approximately one year with a completely dead battery. I jump started the vehicle after a few tries and got it home. I realized that the alternator wasn't charging at 14.2 or better, and the battery wouldn't take a full charge because of a dead cell, so both were replaced, and the car is now starting and running perfectly. The issue I'm having now is the following: With the key in position (2 accessory), I have complete power inside the vehicle ie, horn, turn signals, wipers, radio, windows, ac, etc. As soon as I start the car, I lose all power to everything inside. Again, everything functions properly until I actually start the car, and I am at a complete loss as to why this is happening. ANY advice would be greatly appreciated because other than what was mentioned above, the car doesn't have any other issues. Thank you in advance for your time.