LED lights on the trailer do you mean? If so, I believe you need a resistor in the trailer light circuit to increase the apparent current draw.
A quick Google found this. Haven't read through but I think it's the issue
http://www.vwwatercooled.com.au/foru...ues-31703.html
I reckon it'd be cheaper to put globe lights on the trailer than buy the proper 'dummy load' thing.