Nissan likes to go thru a relay for the trailer wiring connections. Is this to reduce current (amps) thru certain other components? If LED trailer lights are used, amp draw is small and a relay unnecessary in my way of thinking (but am I right?).
You may find it simpler to repair the problem than wire around it.
Let me see if I can walk you thru the steps for the wiring diagram on this forum site:
Just above where your post appears, there is:
Sticky: Service and other Nissan manuals.
In blue letters click on: Service Manual
Go to: Section K Electrical
Go to: LT (Lighting System)
Page LT-64 begins Turn Signals
Page LT-106-115 is for Trailer Towing wiring
Sometimes EBay provides a similar CD manual for a cheep price