Plug-in on dash

On the Peugeot dash, between the writing board and the windscreen there is a small yellow 'thing' (the size of a 5 pence piece and covered by a cap)) that looks as if it takes a plug? It has 3 tiny holes in it. I have looked carefully in the Boxer handbook and can find nothing. Someone on the Forum will know?

Could it be a USB socket to take your iPlayer or MP3 player to play it through the radio ?
We have one in the big drop down locker below the cab radio but it is so well hidden that I couldn't tell you what it looks like.

Thanks for the reply.. Well, we have a usb socket in the drop down compartment too  so unless it;s an additional one?...