Any idea what this is and if it should be plugged into something? 
 

also the big plastic circles with wires going to them under the rear seats, are they something to do with sound system?

There should only be one plastic circle under the rear seat on the off-side and it's the cover of the fuel pump/sender unit.

 

 

Not sure what the plug is.

Edited 5 November, 20196 yr by TMB

So it was the wire for an now none existant cd changer.

 

Thanks TMB yeah is only one side, I was a bit tired. 

Edited 5 November, 20196 yr by alff

Ah, ok.