Re: whats the white wire on a shoreline trailer ?
A faulty ground is probalby responsible for more lighting woes than most any other single cause. I'm my neighborhood's "goto" guy for boating/trailer electrial problems, and bad ground is behind almost all of the problems.
Absolutely correct!
That's why I run grounds from the lights mounting bolts up to the white wire.
Solder all that can be.
Electrical grease on bolt / wire connects (grounds).
Seal all joints w/ 2 layers of liquid tape & shrink tube.
Only probs I have now is an occasional (rare) burnt bulb.
(I play in saltwater)
Yours may never have been hooked up.
Many figure grounding thru the ball is good (it's not!).
Also, paint and galvanize do not conduct elecricity well. If the traier is bolted together, and the connection rust over time,,, finding out why your lights act up can drive you nuts. Run the extra grounds and forget it.