Recently, I asked here, where this spare 12v plug is. I got my answer, so decided to give it a go and connect my GPS.

It took me 5min !!
Removed black plastic cover.
Found the plug.
As my GPS cable has got a line-in fuse I just sided bare ends of my GPS cable into the slots of the plug - job done!!

Insulated all with tape.
Nicely hidden behind plastic cover.
Cover back.
Off you go....