help, puzzled by the radio connector

[Bean]

Hi everyone,

although I like the sound of our engines and it's all I need on a fun drive... there are times I'd like to have a radio.

I looked at the connectors and the schematics for quiet some time and I'm able to connect the new radio but there's still something strange about the wiring



In the bove pic you can see two connectors:
the small on the left is permanent power (+12V fused by 10A in the engine bay)
the blue one is the main connector, the 4 pins on the left side are the two front speakers, the pin on top on the right side is switched (ACC) power (+12V fused by 7.5A in the kick panel) - the two on the bottom are both grounds

the last part is where I'm lost - the wiring schematics in the manual doesn't mention 2 grounding wires, just one.

I wonder if something with my wiring is off, although I'm pretty sure it's genuine as I used to have an original radio in there at one point (wish I still had it). Can anyone verify my findings or knows the reason for the strange fact of two grounding wires?

Thanks in advance Bean