I think its internally connected to the ground on the PCB
i dont have the cab in my house here, so to really verify that, i need to visit my mother...
I did have my two spare boards in my house, and also the converter connector that i have received with the board from Andre,
so i took out the board and checked my theory, and my thoughts where right:

pin 8 does not have a wire connected at the connector as you can see, and on the board the trace goes to a connectionpoint that goes through the board to the other side..

folowing the trace from that connection you see that it goes to points A, B, C, D, and H, which are all ground
The solderside of pin 8 is H and is connected to ground as you can see.
the pinout in the link does not mention "G" and "I", they skipped them, so in fact in the point H = J in the pinout
EDIT:to be more clear, i adjusted the picture with the letters from the pinout :

Hope that clears things up
