Likely the "door closed" micro switch internal to the door lock assembly. I had to recently replace the door lock assembly on my 996 (same as the 986 in this respect) and this solved this issue. I've just had the same thing happen today on the other door, so it looks like I am going to have to replace it too.
BTW, I used a VW Golf Mk5 assembly rather than the Genuine Porsche unit as I could purchase the VW assembly for a fraction of the cost of the Porsche unit. I had to transfer one small external part of the Porsche assembly across to the VW unit, but otherwise it is identical. Look for 3D1 837 015 (Left) or 3D1 837 016 (Right) for LHD cars.
Swap the part circled from the Porsche assembly to the VW assembly:
