1999 ML320 Stereo help!

I bought a new stereo head unit to replace the stock unit (not bose or the touchscreen one). I checked online to see how the harness looked for the 1999 ML320 and I have a question about it. On the stock The wires that were attached to the stock system had 2x8pin connectors where the harness connects to but it also has 1x10pin connector. The harness used only the 2x8pins and i'm just curious on whether the 10pin is necessary. I'm a noobie when it comes cars so please be gentle with the comments.