At a recent family event someone thought that if a car owner installs their own trailer hitch and trailer lights that they void the warranty. Not true.
Pursuant to Magnusson-Moss federal law, any thing you put on your car doesn't void the warranty unless it was the cause of a problem. Only that problem is not warranted. So if you attach trailer lights wrong and that causes the right turn signal to not function, only the right turn signal is not warranted. If the transmission goes, unrelated to the trailer lights, the transmission is still warranted.