Our driver had refused all strong drinks because he wanted to be sober for the trip home.
Is the past perfect tense used correctly here?
I think that the action "want" occured before the action "refuse" ,and therefore we have to say something like this:
Our driver refused all strong drinks because he had wanted to be sober for the trip home.
No. If you say "he had wanted to be sober" it suggests that that situation changed and at some point he didn't care if he stayed sober or not.
Our driver refused all drinks because he wanted to stay sober to drive home.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.