T-One wiring harness

Anybody ever have any trouble with an after-market wiring harness?
I've got an '06 Mazda Tribute that did not come with a factory tow package. So last fall I installed a T-One wiring harness that I bought on-line (Drawtite.com)

When we picked up the camper, it worked just fine, and also for each of the next 5 or 6 trips we took, spanning from Nov '11 through about July '12. Then, when we hooked it up one time there was an open circuit on one of the turn signals--it wouldn't come on.

I didn't want to think that with after-market harness I installed was bad, but everything I checked pointed to that. So after checking everything else I could think of, I went on-line and bought another T-One harness (from e-Trailers.com this time)

I swapped out the harnesses, and it all worked right again. Good news, I thought. We took a 2-week trip up to Maine (from FL) and it all worked fine. Then we were home for a week, and when I hooked it up again this morning, there was a short in one of the brake lights--it wouldn't go off.

Everything I checked pointed to another bad harness. (it's not just a wire harness--there is a potted electronics module in there too). So I took it to an auto electric specialist, and they said that the T-One harnesses you buy on line are kind of light-duty products, and this trailer has enough of a load that it requires an HD (heavy duty) electronics module in the harness.

Anybody ever had any similar problems? (Apparently the Mazda Tribute has had some issues of its own in this area, and I didn't know that either...)