Trailer Exterior Lights: the most common trailer problem

The single most common problem with trailers in general is the rear lights. Trailers and automobiles typically use a frame ground. Cars are enclosed, so a ground to the chassis typically causes fewer problems.
But trailers, especially kit trailers, use an exposed wiring harness and they ground to the frame.
The wiring and the frame are exposed to the weather, road salts, corrosion, excessive vibration and foreign object damage. Inevitably the connections suffer and the lights begin to fail. If we are trying to boondock camp in our trailer or ninja camp in town, we don't want to draw the wrong kind of attention from the Law. Being stealthy means NOT drawing attention, and making every effort  to blend in. Tail lights being out is a famous way to draw attention from bored cops.


If you have had a light failure even though your voltmeter shows 12v at the socket, you've been on the receiving end of one of these problems. Running a new ground to the attachment point of the light from the harness plug will probably fix the issue. 
Much of these problems can be mitigated by switching to lower-current LEDs, and enclosing the wiring in flexible conduit when you run the harness for the trailer. While you are at it, run a separate ground wire (white) to each rear light from the harness plug.

In this case, I ran flexible conduit to the rear and to the opposite side of our tiny house trailer. All of the trailer exterior lighting that connects to the tow vehicle is below the deck. All of the interior power runs are in conduit above the trailer deck. I'll discuss the details of the dual-voltage  interior wiring and lighting in a few future articles,but for now we will stick to the standard trailer lights.
The goal was to have no accidental cross-connections to the interior power circuits and to be able to inspect or work on the exterior lighting without having to tear into the structure or pull up the decking and insulation.
In addition, I built a removable rear panel and needed the rear lights to be capable of disconnecting from the harness to make access and repair easier. 

The enclosed lower half of the deck before I laid on the side panels and sealed up the deck side trusses. The circuit boxes are bolted to the back half of the tongue frame supports through existing holes in them, which made things easier. The 1/4 ply just slid under the boxes and was bolted to the frame cross members, and any previously cut zip ties for the conduit were replaced.

Once I got around to installing the lights, I replaced the cheap incandescent lighting with LEDs. The LEDs will run on far less power (so issues like corrosion will matter less) and burn out less often.

Tags: Trailer light issues, Stealthy tiny house, Boondocking trailer, DiY exterior lights, DiY trailer lights, Stealthy trailer lights, Avoiding trailer light issues, Most common trailer problems, Wiring trailer lights, trailer light conduit.