You Could try disconnect the battery over night and see if that resets the light failing this diagnostics will be needed incase it's a faulty sensor.
Reason I ask about the speedo is the mk6 is prone to frying the abs module this happened in my girlfriends car two month out its warranty period but if it goes you don't get a speedo reading as this is done through the abs sensors. Maybe you have knocked a wire or something When running your power cable for your amp so I would also check connection on abs module