You don't say what TV you have. Many new TVs have the Aux 12V line to the Bargman connector installed, but do not install the fuse ( and if used relay) in the fuse block. Some even supply them in a zip lock bag in the glove box. That being said, the gauge of the wire used in the OEM wire harness is marginal at best. If nothing is on in the 5er you will get some minimal battery charging while traveling at highway speeds. If you are running other stuff ( fridge control) you will get virtually no charge. The voltage drop between TV and 5er causes this problem. If you need some charging capability, run a new #10 wire from fuse block to Bargman for the 12V aux line. Also be sure the dealer uses #10 wire when extending you connection to the bed. To see how you are doing, measure the voltage on the 12V pin of the TV bargman while under about 10A load. You can see as much as 2V drop.
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