JMHO from years of having trailers. Most problems I have run into have been grounding issues.
Very true. That's why most of us who've had problems in the past recommend running ground wires from the plug to the lights, not grounding through the frame. Frame grounding seems like it would work fine but most grounding problems seem to show up there.
Even worse is grounding through the hitch ball. Those always seem to fail when things get dirty.
