A Handy Tester for Trailer Lights

‘Tis the season for using my boat trailer. But first, I need to test whether the lights work.

Trailer light wiring breaks easily, what with vibration, corrosion, and mice chewing on the wires. To test your lights, you can drive your vehicle over to your trailer and plug it in, or buy a hefty, expensive tester, or make this small, inexpensive tester.