The car docking sled does not have an ethernet port on it. Oh, they wanted one all right, but there just weren't any docking connectors with enough pins.

So they did the next best thing: They left a hole in the docking sled so you could put an ethernet cable in there if you wanted.

The only problem is getting it to dock reliably. This is tricky. Some folks simply leave some slack in the ethernet cable behind the sled, pull it out through the sled hole, plug it directly into the player, then insert the player into the sled. This works, even if it's not ideal.

If you're set on making docked ethernet, the first thing is to remember to break the keeper tab off the plug or your player might end up permanently docked.

Then, you need to find a way to rigidly support the plug while still being able to adjust it so that it docks reliably every time. This is the hard part. Some have done it by carefully tying the ethernet cable to a piece of a metal bracket using cable ties. Here are two examples of docked ethernet, courtesy of BMihulka and CharcoalGray99 from the Unofficial Empeg BBS: