Does the lights still flicker if you use the light learning switch in the cab after you have initially coupled the unit? I seem to remember the unit recognises the presence of a trailer through the indicator circuit resistance. LED lamps are low current draw but usually have a resistor to up the current draw for light failure systems. We were told you need to do a light test every time you swap trailers, which includes checking all the trailer lights work so, two birds with one stone.