This is the primary cause of trailer-light problems. Symptoms include flickering, fast-blinking, dimness, intermittent operation (often when a trailer ball is used for a ground), and complete failure.
Searching for the right trailer wiring can be tiresome. There are many industry standards that don't lend themselves useful to the layman. Every standard is there for a reason, so don't go wiring your ...
A brake controller makes a trailer stop more like a car. There are hundreds, maybe thousands of accessories for trailering, but nothing makes a bigger difference than the best trailer brake controller ...