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Old 12-23-2022, 05:07 AM   #1
DougVelting
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M.O.C. #27691
Tail Light On For No Reason?

Has anyone else come across this that can point me in a direction to look?
My passenger tail light on our 381TH comes on when it rains. We are stationary for over a month now, no truck hooked to it, no other lights on.
Its been raining here for a week, and the last time it happened i believe it was raining. I just dont want to crawl through 40 feet of mud tracing wires if someone knows where i should look first
Doug
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Old 12-23-2022, 07:28 AM   #2
ChuckS
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M.O.C. #20949
This PDF should give you all the info you need to TS your light issue.. I would start right at the 7 way connector and then move to the pin box. There is 12 volts present on that RV side 7 way plug all the time and it sounds like the wire or strand of wire from the 12 volt wire is touching the wire for the passenger side tail light..

Your issue will be in this area.
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Old 12-23-2022, 07:31 AM   #3
Daryles
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M.O.C. #24086
The wiring junction for the right tail light is behind the left tail light.
Hope this diagram helps.
You will need a multimeter.
I suspect water intrusion in the 7 way cable junction box. That's the only 12v source (coming from the battery to the emergency brake away switch).
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Old 12-23-2022, 07:38 AM   #4
DougVelting
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M.O.C. #27691
That's where i was going to check first. I had the trailer plug draped over the 5th wheel and was thinking maybe the plug is just wet and shorting. ive moved it to inside the little cubby hole in the back of it. Was going to check the junction box after the rain lets up. Thank you for the wiring diagram!
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Old 12-23-2022, 08:37 AM   #5
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I agree with the above comments. BUT. The two taillights are supposed to be connected to a common wire from the 7 pin connector. Odd that only one would be on. First question is, do both taillights come on if you jumper pins 3 and 4 together at the 7 pin connector? If they both come on, then the question on only one coming on like that is even more vexing.
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Old 12-23-2022, 08:55 AM   #6
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This is very odd. The tail lights and ALL running lights are tied together, so one would think that if a hot was applied to any of them they would all light up. Seems to me I recall back in the day an issue with a feed back problem caused by a faulty ground that caused a single tail light to illuminate....can't recall the details but probably not relevant anyway. Good luck.
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Old 12-23-2022, 10:29 AM   #7
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M.O.C. #20477
It may be a brake/turn signal light instead of a tail light as they are wired independently. Would still start at the rig's 7 way plug.
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Old 12-23-2022, 12:51 PM   #8
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I don't know if this will solve anything or not, but... could you back up your tow vehicle to the trailer and plug in the umbilical cord, turn on your vehicle lights. Run a quick test of the brake lights, turn signals, and running lights (4 way flashers too). Turn lights on and off. If all the lights respond correctly as expected, then unplug again. Stranger things have happened, I'm sure, but maybe the light won't come on again after doing that (but maybe it will). Anyway, plugging back into the tow vehicle will either help you assist the problem or make things even more confusing.
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Old 12-25-2022, 10:30 AM   #9
Hblick48
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M.O.C. #21903
Odd chance:

Previous owner had rear view camera. Wired the one warning light to 12 volt full time and wired camera to that wire.
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Old 12-25-2022, 02:13 PM   #10
Mark7
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Im betting a problem in the plug. Maybe even water. The right T/S and 12 volt battery wire are right next to each other in that plug.
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Old 12-28-2022, 07:12 AM   #11
DougVelting
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M.O.C. #27691
Well best i can tell is that it was water in the 7 way.
Took it apart and nothing jumped out at me right away.
Used compressed air to blow into all the connections, tucked it into the cubby out of the rain and it seems to have gone away.
Thanks all!
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