I've always suspected trailer wiring of being irrationally complex
Here's my conundrum: there are two identical (same model / type / manuf) LED lights. They are connected as shown. One will light and the other will show only a single LED in the center. Car end is toward the left.
Black is a duplicate ground that I run in addition to the actual ground. At each fixture, both types of ground are interconnected. Hard to believe that either fixture gets a different ground level from the other (Port will light even if connected only to the frame).
Red is the connection from the car (in real world color schemes, the brown cable). The diagram shows the port light tapping into the connection to the SB light. Should give same voltage to both.
But Port absolutely won't light fully when SB does.
Anything I should try?