You might consider purchasing a new plug, and rewiring the trailer circuits to match the pole pins of your truck's plug. That way you will ensure each trailer function is properly sourced. With a used trailer, you have no way, other than operation, to know if the original owner had changed any of the voltage sources that might be incompatible with your truck.

Many times people will just install the wires by their function within the plug, and not follow any standard wiring placements. That combination can work well for that owner, but when towed by another vehicle, that trailer's lights and brakes can become inoperative.

As was stated, there are several wiring diagrams available on the Internet, that will show the proper (standard) placement of the leads within the type of plug you are using. It is not difficult to individually power each of the trailer's wires to determine what circuit they feed. As each one is determined and placed within the plug, the remaining wires are easier to identify. If you use a power source such as a battery charger to illuminate the circuits, you will eliminate the chances of blowing your truck's fuses.

A multi meter will determine what circuits your truck's pin are activating, and it's then an easy task to match the trailer wiring to them once they have been identified.

If a LQ was added it is possible that alterations were made to the trailer's original wiring. You would think that interior alterations would not affect running, turn and brake lights, but the main looms often run within the interior framework, and may altered during the interior's addition.

 Again, using a power source to each pin can determine what circuits the wire is feeding. It's much easier to trouble shoot this way, than trying to use the colour coding of the wiring, which functions can vary from manufacturer to manufacturer.