how long are you bulbs lasting before they're "fried"?
What you're describing for the installation sounds just fine. As far as I know all of the fog bulbs used in the recent VW's are 55W. Switching the plugs for the different bulbs just changes where the wires go and has nothing to do with power. If your harness is truly killing bulbs then it would be something like a short, cheap relays that screw up the power some how, etc.
I went through two sets of rather expensive Hella yellow bulbs in my fogs.. each set lasted around 2 - 3 months. I went to the Ziza bulbs that ECS sells and that set lasted around 1.5 years (my fogs are on quite a bit). In that case it was just the bulbs.
As another example, the last couple of sets of license plate light bulbs I bought have lasted maybe a month at the most.. where as the factory provided set probably lasted almost two years.
So, unless you're bulbs are burning out almost immediately, I wouldn't discount that you're just using crappy bulbs.