You have to cut the J19 wire and screw one end to "stand/side" and the other end to "Tam MFC-01".
See also p. 2 of manual.
I have the same problem I have two other trucks with the same unit the the trailer tail lights work properly
they are all wired the same
Is my unit faulty the bec voltage is 5V and the light voltage is 3.7V and 4,2V
I was told to put a resistor from several hundred ohms to 1.2 k between the light and stand/side but it didn't work
