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Old 07-10-2006, 09:42 PM   #1
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ft collins , Colorado
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Step on brakes and trailer lights turn...OFF

Anyone seen this before?

Two nights ago I changed out a couple of clearance lights. Everything working great. Tonight I turned on the lights in the vehicle to show my wife the lights and they are on but it looks like a brown out. They are getting juce, just not enough. Then I notice the brake lights are on constantly on the trailer. When I step on the brake they then turn OFF. However if the lights on the vehicle are off the brake lights light up just fine.... Any electrical whizes out there? Thanks for your help.


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Old 07-10-2006, 10:20 PM   #2
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1978 31' Excella 500
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Looks like a ground loop. Revisit the clearance lights and any other fixtures you worked on.

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Old 07-10-2006, 10:23 PM   #3
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2006 25' Safari FB SE
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My guess

Well, I am no electrical wiz, but, your clearance lights and your brake lights require power through your TV 7 pin connector. Your interior lights are internal wired and should not be in line with either brake or clearance lamps.

I would recheck the clearance lamps you worked on and the 7 pin connector. It is possible that some kind of short discharged your AS and TV batteries, which of course would make your AS interior lights very dim if not off. If your AS battery was depleted (drained), then it is possible that the application of the brake sends more current to the brake lights and thus dropping the current to the AS turing the lights off.

Just my guess! Maybe an expert knows the answer for sure.

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Old 07-10-2006, 11:19 PM   #4
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ft collins , Colorado
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Can you tell me more about the ground loop? Can I tell with a volt meter?


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Old 07-11-2006, 05:20 AM   #5
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1989 34' Excella
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This is a job that requires some electrical knowledge. You either have to learn it yourself or find someone to help you out. It would be better to do the latter. Have an electrician friend help you out.
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Old 07-11-2006, 05:28 AM   #6
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You may have a bad ground from the tow vehicle to the trailer. Your clearance lights may be using all the ground the bad connection can carry, and when you step on the brakes, it overloads the ground and shuts all the lights off. Check the 7 pin connector, then the ground wire on both the trailer and the tow vehicle.
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Old 07-11-2006, 08:02 AM   #7
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ft collins , Colorado
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Okay so this morning I went out and connected the trailer to the hitch and Everything works Great! Why would connecting the trailer to the hitch do anything? Does it complete the ground?
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Old 07-11-2006, 08:16 AM   #8
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Originally Posted by bridger
Okay so this morning I went out and connected the trailer to the hitch and Everything works Great! Why would connecting the trailer to the hitch do anything? Does it complete the ground?
Yes it is but it shouldn't be. The ground circuit for the trailer comes through the wiring plug connector. One of the 7 wires is ground for trailer and truck. It's obvious this circuit is open. Keep in mind the poor ground { throught the trailer ball} to the lights is also the POOR ground for the trailer BRAKES !!!!! The brakes require more current than do the lights and with grease or rust at the hitch connection you are in danger of having trailer brake failure
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Old 07-11-2006, 11:57 AM   #9
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This one is EASY. Just as Mike Lewis said, there is a problem with your seven wire connector and it is either in your tow vehicle or your trailer. You have a loose or mostly broken negative ground wire. First, take your 7 pin plug, the one attached to the trailer and take it apart. It's easy, a couple of screws and the cover comes off. Look for a wire to have pulled loose from the screw terminals in there, especially I believe a white one. Replace any that are loose. Look for broken ones, repair those as well. Did this fix it?

If not, get a multimeter, with a continuity tester built in; I like the ones that give a tone when a ciruit is made. You can get one at Home depot for about $15. Look up the pin placement for the connector, there's a website at Mark's RV that has it. Turn your mulitmeter to continuity and then poke or clip one wire onto your bumper(actually, it must be metal, I guess not too many metal bumpers anymore!) of your car and then poke the other one in the negative ground recepticle on your 7-pin connector. Should have continuity. If not, the problem is in your car. If this works, then check your trailer. That should be the prolem. Follow the negative ground from the plug, to the access panel on the underside of the trailer, should be a removable panel underneath, up front, by where the A-frame meets the body. Follow the wires until you find a broken one.

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Old 07-11-2006, 09:32 PM   #10
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santa barbara , California
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Hello bridger,

electricity will find the quickes path to ground .In your trailers case your
plug ground somewhere is missing as has been posted .A poor ground ,corrosion or loose connection will cause dim lights ,such as if your
car headlights ,older ones these days with the standard 3 prong plug,
is dim when the headlights are on ,as we have all seen one time or another,
you wiggle the plug and then the headlight goes bright .The ground wire is faulty . On trailers those poor grounds cause the electricity to travel
the path of least resistance ,as in your kooky operation of the brake lights and running lights .Get a solid connection as when you hitched up .all
returned to normal ,the lighting ,brake lights all suddenly work right.So
as everyone has said here ,locate the faulty ground ,be careful on these
types of problems ,because its easy to get off track ,replacing bulbs and
stuff .Dim lighting ,bad ground and other gremlins related to it.


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