I just picked up an OEM Nav unit and I can't figure out where this piece goes or what it's for. I know where it plugs in as the cables are really easy to figure out, but I didn't see anywhere in the dash where it belongs. Can anyone help me out with this?

 

That is the CAN bus grounding interface. It bolts to the bottom of the cage that holds the radio. Cables run from the radio to this interface box, and then from this box connect to the car.

 

So the metal thing on the left in the picture below? It attaches to that?

Also, the box only has one plug which hooks up to the Navi. There's no other way the box connects to the car.

 

I got my question answered. This box mounts to the metal harness in the picture above that I posted. It goes along the horizontal bottom piece of it. The little box itself needs to brackets on it to allow for it to be mounted on the metal harness.

 

Full How-To: https://www.evolutionm.net/forums/ev...-evo-10-a.html