Unexpected Tail Light Illumination

[TXWind]

Why are some of my rear trailer lights on, although very dimly?

My trailer is currently on shore power and not connected to my vehicle.

The two pictures are trying to show which tail lights are dim but on.

I have not seen this before and curious if someone can explain what is happening.

When the towing electrical harness is connected all is normal. Turn signal, running lights, brakes lights, and completely turned off works as expected.

I have experimented various configurations of AC off and my battery disconnect switch in "use" and "store". None of these changes impacted the lights that are on.

My pictures are both of the right rear quadrant but it is the same on the left side but mirrored.

Some additional background. I got a lot of rain last night. Last week my trailer was in the shop for warranty work on my smaller air conditioner and I was told that several electrical diagnostics test were done. While I suspect an electrical short of some type from the rain I don't want eliminate any possibilities until I can eliminate it with confidence.

Does anyone know what is going on or has suggestions on diagnostics?

Thanks in advance for the responses!


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[mimiandrews]

I'd check the U-cord's plug wiring first.

Could be a stray wire strand within the U-cord connector is feeding power from the trailer's battery to those lights. If the U-cord is not plugged into the TV, there's no other possible power source--unless the wires for that light are close enough to an AC circuit for induction to happen or something really strange like that.

[DanB]

You probably have a backfeed thru ground.

Disconnect and remove batteries. See what happens.

Disconnect shore power, try again.

[Protagonist]

If the lights are LEDs, that might have something to do with it. A very small current can be enough to light up LEDs when it wouldn't be enough to make an incandescent lamp glow at all. I'm inclined to agree with the induction current theory as the source; it doesn't have to be a short, just AC and DC wiring in too close proximity parallel to each other.

[richinny]

i think someone here posted the same thing was caused bby a damp umbilical cord plug.

[PaulnGina]

Originally Posted by richinny

i think someone here posted the same thing was caused bby a damp umbilical cord plug.

Yes. Based on that post, I started wrapping the end of our cord in a small zip-loc bag, sealing it off with a piece of velcro. Then I make sure to store it with the open end of the bag pointed down so water doesn't seep in.

[Arcticfox]

I have seen the exact same situation with my trailer. Have no idea what is causing it but I've seen it myself


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[bradt]

I think this looks familiar. I had this same partial illumination of LED tail lights with a horse trailer. And it cleared up with dry weather. The clue is the partial illumination. LED's have slightly varying turn on voltages. The tail lights have multiple strings of LED's, when there is leakage current getting into the wiring, the most sensitive LED will begin to conduct and faintly illuminate. It hogs all the leakage current and there is not enough to reach the voltage threshold of the other LED's.
Look for dirt and moisture in the 7-pin connector. There is one pin with 12v on it that could supply the leakage. Also look for moisture along the path of the taillight wiring. It is a tiny amount of leakage that should go away when it drys. I hope that will be your case.
Look for this problem to show up in other places as we convert to LED lights that use such tiny amounts of current. Leakage was not an issue with the wiring and connectors used with incandescent lights.
I found a covered 7-pin connector storage clip that fits on the tongue jack column. HUSKY part #81497. It keeps the connector end dry and off the ground.

[Minipad]

1) Carefully disconnect the negative cable to one of your batteries and see if the lights go out. If they do, the problem is most likely in the umbilical cord. If it is a new trailer, the cord likely has a molded plug which means you can't remove the plug to inspect the wiring. Reconnect the negative cable on the battery and then take a blow dryer and warm/dry the plug and that may tell you if the problem is the suspected moisture. The second suspected location for an umbilical cord problem would be were it connects to the junction panel on the trailer. (Most likely under a cabinet in your trailer.)

2) If #1 yields no change and your trailer has two receptacles for the shore power, try swapping to the other receptacle and see if there is any change. If your shore power is connected to the receptacle near the lights, it is possible that the small voltage drop achieved from moving the plug, may tell you if the AC/DC parallel wiring is suspect.

On a side note, on every new trailer I acquire, I immediately remove the umbilical cord plug and wire the end of the wire into a "nose box." I place the nose box on the forward surface of the battery box. Then I build a 3' to 4' whip to connect the nose box to my tow vehicle. This is standard procedure for the electrical connection on semi-trailers and for good reason. Umbilical cords consistently fail. It is much easier to replace the whip cord instead of having to rewire a plug when issues arrive. I carry an extra whip and it has saved me more than once from making roadside repairs, usually in a snow storm, to the plug on the umbilical cord.

Good luck.

[PecanMan5]

Mine did it. Rain water got in my connector. I now keep it covered.

[bwpaint]

Originally Posted by PecanMan5

Mine did it. Rain water got in my connector. I now keep it covered.

Mine too.

[TXWind]

Thank you all for the responses.

Yes, it is a new trailer with LED lighting. Physically disconnecting the battery does eliminate the problem. Plugging the trailer into my SUV also solves the problem.

While the lights are still on right now I am monitoring them for when they go out to see if it is tied to when everything drys out.

Since I have removed AC power from the trailer in multiple power configurations I do not suspect that inductance is the issue at hand.

Because of my hitch, I do have second short umbilical harness to reach my SUV which just increases the potential for what I will describe as voltage leakage.

Finally, thank you all for the suggestions to prevent a reoccurrence in the future.




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[Minipad]

I feed the break-away brake wire and umbilical cord up through the bottom of my propane tank cover. I loop the wire through the handle on the propane bottle and then use the loop on the end to hold the plug of the umbilical cord. Keeps it nice and dry.