Original owner 01 Xterra - Ordered with tow package. 9 years later I buy a boat and trailer but when I plug in the tow harness from the trailer to the truck I get the following.
Brake lights work, right turn signal works but the left turn signal does not work. (useing a 4 pin tester) I have checked all fuses, bought a new harness to plug in under rear wheel and same issue - everything works but the left turn signal.

Any ideas? Someone said check the controller for the trailer lights is located in the passenger compartment behind the panel on the lower right hand side but which one is it and how do you test it.

Thank you in advance!

possibly the trailer?

Left turn signal will not work with the tester or when the trailer is hooked up.

Bump....Any input please. I can't register my boat trailer unless this is fixed.