2008 Quest Trailer Wiring

[snyder.ct]

I have no been through 3 trailer wiring power converters, all installed by the dealer and all have been fried. Trailer lights stay on (sometimes with key out of ignition) when the issue occurs. Just in case it was the trailer, I tried another one on the latest converter and had the same result. The lights all work fine initially, but at some point I notice they stay on, with no signals or hazards. The converter is a hoppy powered unit, is the dealer installing the wrong part? They told me Nissan doesn't make a converter and they don't know what to do next. Being that I negotiated the harness installation into the deal when I bought the van I feel they owe me a functioning wiring harness. (They charged me labor on the last replacement but I talked them into splitting it 50%)