Nope, seriously, Vauxhall do not actually install the wiring any more for these things.

A bit like new Zafira's with roof bars, if you do not specifiy it when purchasing new, then you can't have it. Vauxhall even modified the shell on the Zafira to prevent it.

You're best bet would be to get a 17A (or bigger) wire and run it back to the fusebox where the connection would be.

If not, let me know and I will check with the lads in work about it as I work for Vauxhall.