Where's your amp and your radio?
The amp (if still there) would be mounted in bracket in the rear left compartment. Several audio/nav components are all packed in there together...but in their own brackets. See
A18 in pic below...that's where the amp should be:
If you have the nav screen up front...the radio (BM53 or BM54) is in the rear next to the battery (in the same compartment):