You pretty have to expect to get raped by the dealer. If they didn't fix the problem the first time, I would demand that you should not have to pay for the first repair, and for them to try a second fix.
As far as the electrical problem goes, your guess is as good as mine. It does sound like a harness issue but if you've already replaced it you need to check other points in the harness farther into the circuit. Fuses? Defective bulbs?
Be aware that any time you exceed the wattage of any electrical component, you're going to have to deal with issues of heat and therefore melting (I'm an electrical engineering major). Lord knows how many times I've melted capacitors by not using proper wattage. Also check and see that all parts of your harness (the WHOLE harness) is properly insulated. A grounded wire is one of the easiest problems to fix, but one of the hardest to diagnose because you have to inspect every inch of the wire. Check especially where the harness is around any moving parts, sharp exposed metal, pinching, etc... Of course going back to my original argument, the dealership should be able to find and diagnose the problem and if they do any work that does not fix it, you shouldn't have to pay for it.