If I unclip the removeable panel which gives access to the left rear lights, lowdown I can see a large black curved plastic box with a switch velcroed to it.
Anybody any idea what they might be?

 

Not to sure does it have a trailer harness?

 

Yes my Sept 2002 V70 does have a towbar and electrics.

If I reach under the plastic box I can feel that it has no base; nor can I feel anything inside it.

Davy

 

Any way you can take a picture and post it?

 

It's a vent to the inner rear fender. If you remove the bumper cover ever you'll see louvers.

 

Ah, maybe its a cowl for venting battery fumes?

But I wonder what the switch is for?

 

shouldn't be for battery fumes, thats why volvo uses the special type with hookup for vent tube through the floor. Almost any car I've owned has had some sort of vent there. I found it first in my Monte Carlo, my 12" sub was making a funny sound in the fender...found it it was the louvers in the vent flapping.