It's standard: You overkill the positive side of the 12-volt circuit andignore the ground circuit. Basic electrical circuit design requires acomplete path back to the battery through the ground ...

Don’t be one of those people who saves money by sizing conductors only as large as you have to (by Code), but then turns around and recommends a big investment in a new lighting system to save energy.

As a fundamental concept of electronic design, voltage drop ranks highly as one to understand well. I particularly appreciate when industry folks come up with creative ways to get the point across.