djomlas,
Sorry, can't help with the convertible top, but are you sure the light that is on is for the rear trunk ? There is also a light when you start up the car that lets you know the retractable spoiler is working correctly. It will not shut off until you drive the car forward. The first day I had my Box I thought the light was for the rear trunk as well. That night I read the owners manual and found out it was for the spoiler
Hope this helps...
Nick