It sounds like the guy only did the job halfway. Is the generator a 12v generator or a 6v generator?
Wire can be purchased at the local parts store or the internet. Doesn't matter. 6v should be 12 gauge wire. I'd use 12 gauge for 12v too even though 14 or 16 ga can be used.
There are several companies that produce complete wiring harnesses but it would be pretty easy for you do do it yourself, one circuit at a time.
