Weird electrical problem

[billmoore]

Tonight I was hitching up the trailer in the dark and noticed that one of my tail lights has 8 of it's 11 LEDs always on, just a very dim glow. Not noticeable in daylight, but when it is dark you can see that they are on. Nowhere near as bright as when the tow vehicles headlights are turned on (which powers up all 11 of them).

So I disconnected the tow vehicle, and they were still on. Unplugged shore power, still on. Hit my battery disconnect switch, and they go out. Turn the disconnect switch back on, they light up again.

So I have no idea how long they have been this way, maybe all along. We've found that when boondocking our battery goes down way faster than other people claim to get out of theirs (max of 3 days with very light usage, 1 day with heavy usage). This was what led us to purchase a generator.

So... I guess I'm going to have to tear into the wiring and figure out what is going on. Anyone had anything similar, or have any ideas on where to start?

[billmoore]

I'm referring to the vertical tail light on the right midway up the back of the trailer in the photo above...

[pjcd]

Not much experience with electrical issues, but I would think its grounding out someplace, just a guess.

[Merlin]

Good detective work so far. Trailer wiring is such a nemesis! The wiring for the 7-pin trailer light connector goes to a junction box on the frame under the tongue. I wonder if on the toy haulers, those rear door lights have their own wire from that junction box? Seems unlikely, but maybe start there and look for a single stray wire shorting out to the battery positive screw connection. LEDs are weird lights. The dimmers I installed on the LEDs over the beds caused a tiny flicker in the lights, even when off. It takes very little stray current to dimly light an LED, and some are more sensitive than others. Still, those taillights on yours should not be on at all, so somewhere a tiny bit of current is leaking over to the positive wire.

[DavidM]

Merlin is spot on. It takes maybe a hundredth of an amp to dimly light LEDs. As he notes, look inside the junction box on the tongue. It only takes a little wet spider web or similar to provide that much current to the tail/clearance light circuit.

If that isn't it, then follow the wire from pin 3 (the black wire typically) on the trailer connector through the junction box and underneath the trailer. It will branch off for clearance lights on the side and then head to the back. Somewhere the wire may have chaffed against another that is positive all of the time, like the main DC feed from the battery to the converter. In fact if there is nothing wrong inside the junction box, I would follow that wire back first and see if there are any problems with it.

You can also pull the fuses in the converter box one by one to see if one kills the LEDs. Then it is that branch circuit that is somehow crossed with the tail lights.

I also doubt that this is by itself is causing your batteries to drop too fast. The current is too low. But it may be related to another DC fault to ground that is draining your batteries.

See the attachment for pin 3.

David

[billmoore]

Thanks guys! It will be a few weeks before I can tear into it to investigate further. I'm dropping it off at my son's house this morning so he can use it as a cargo trailer - they are moving to a new house next weekend. Probably will have some time to look at it around the holidays.

Good to know about that junction box, I will start there!

[Chappy133]

I have phantom power loss in our camper. Problem solved for storage with a battery kill switch.

[billmoore]

Yeah I have a battery disconnect switch, and always disconnect for storage.

[craigd]

Did you pull the light in question and check to see if there are any aluminum shaving in there. I had one light inside my camper that would come on by itself and the shavings were the issue.

[DavidM]

LED lights come on inside the camper when aluminum shavings short the on/off switch.

With the trailer unplugged from the TV, there should be no power going to the tail lights and there is no switch. Something external to the lights is supplying power like a chaffed wire to dimly light them.

David

[Merlin]

Unless a bunch of Al shavings dump out of the junction box on the tongue when Bill takes the cover off! Unlikely, but stranger things have happened.......

[billmoore]

I haven't pulled the light itself, but if the junction box yields no clues, I may end up having to do that to trace the wires looking for a short...