Danno,

I just recalled that, while I did have a problem with my converter box, that I was also suffering a voltage drop through my old crusty trailer wiring. The old incandescent lights worked fine but were a little dim. I had just replaced my converter and still couldn't get the LEDs to function properly. They flashed but it wasn't all the lights and it went from dim to dimmer (or something like that). The side markers, which are separate LEDs on these, also didn't function properly. I tested them by touching battery terminals and they worked fine.

In my case, I had already planned to redo all the trailer wiring anyway since I had suffered a couple of shorts over time and I did that afternoon - soldering, applying sealant, and shrink wrapping every connection as I went. They work perfectly after that. They are nearly blindingly bright at night.