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Discussion Starter · #1 ·
We refitted our 5 x 10 utility trailer with all new lights and a new wiring harness because the original lights and wiring were in pretty rough shape and there were some pinched/broken wires and rusty connections etc. All the new stuff works well, lights are nice and bright. Here's the problem: with the truck's lights turned on, all of the trailer lights are also on (as they should be) until you hit the brakes. Then, instead of the trailer's brake lights coming on, ALL trailer lights go out. The brake lights on the truck come-on okay, but the trailer goes dark. When the lights of the truck are off, as in daytime running, the trailer brake lights work as they should when the brake pedal is pushed. The truck brake lights always work. This is a pretty basic wiring scheme so I'm not sure where the problem could be. And, this situation could be especially hazardous for night driving. Any help with this problem is appreciated. Thanks
 

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Number One thing to check would be that you have a good ground for the lights... I've noticed that lack of a solid frame ground can lead to some pretty wacky light behaviour. I had a loose ground on ONE tail light, so that when I had the trailer lights ON, both tail lights worked, but as soon as I turned on the turn signal for one, the other light (with the bad ground) would go out. I know they're new lights, so it SHOULDN'T be, but.... Check for rust around your ground points etc...
 

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Second that on the ground make sure you have the trailer grounded to the truck and are using the white ground also
 

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Discussion Starter · #4 ·
Thank you for the prompt replies. I agree that grounds can be a real gremlin on electrical problems. I'll go back through and check/clean grounding points. The white wire is connected properly. I guess what puzzles me is that the lights work flawlessly except in the one circumstance I described in my original post. Thanks again for the help.
 

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is it by chance a ford truck? they don't ground the white wire in the harness and you have to run one to it. that or use a clip on wire to replace it. my trailer works perfectly fine on every vehicle it hook it to except a ford, i always have to run a temporary ground from trailer frame to truck frame when i pull it with a ford. i may be off base on this one, but this has been my experience with this and several other trailers.
 

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What happens when you turn on the turn signal ?
They are using the same circuit as the brake lamps so it should help you determine if this is an issue from the truck side or the trailer side. If everything works fine with turn signals on (try the hazard flashers also) then you may have an issue from the truck.

Note that some trucks have a circuit breaker for the trailer lights. If you have a short in the wiring for the brake lights it may cut out and then automatically turn back on when you release the brakes.
 

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I used to use removable a wooden light bar on boat trailers so we ran the white wire all the way back. You could try that temporarily in order to isolate the problem.

This is probably obvious and a dumb question, but you are hitched up right?
 

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I currently own two utility trailers, and have 3 others in the past,,,,when you have problems with trailer electrical gremlins,,,,,go to TSC,for 25 dollars you can buy a complete trailer lighting kit ,,,two lights ,clearance lights ,wiring and the male and female plug ends..Throw the old wiring on the ground and insall the new lights and wiring,,,,save your self a huge amount of time, greif, :thThumbsU
 

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Discussion Starter · #9 ·
Thanks for the continued suggestions and replies. (davidg) This is a Dodge Dakota, but I'll still check for the ground you are refering to. Like other replies here, I think it's a ground problem somewhere. (Alan Lloys) I didn't think to check the turn signals or flashers simultaneously with the brake light malfunction, but I'll try that and see what happens. And I didn't know about a circuit breaker in the trailer light harness on the truck. Not sure where I'd look to find it, either, but I'll poke around. (rwall10597) I thought about running an individual white wire to each light. Not sure if I want to go there, yet, but I may end-up doing that. (deereboy55) This is all new stuff..new lights, new harness, new, plugs, so I don't think it's the lights themselves, but I guess it could be. I have to think the lights and harness are good. For now, we put the trailer back in the out-building, it's snowing and turning colder, so we'll have to wait for a little better day to get back on it. Thanks again for all of your help.
 

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Its got to be a ground issue.

If the tailer is a tilt bed run your ground to the bed of the trailer to ground it, sometimes the piviot between the frame and bed you can lose your ground.

Now IIRC you can only hook your wire up (no hitch or safety chains) that way there is no chance of it grounding on your trailer ball, and then check your lights, if they dont work than it could also be the ground on your truck.

just a tech tip but I never check my trailer lights with it hitched to my truck, it insures that the ground on the plugs is right, also always check 2 functions at once like lights and turn siginal or brake and turn etc etc. I also carry a set of mag mount lights in my tool box just incase ...... I know every hillbilly around here has no clue what trailer lights are, but with my luck I would get busted for no lights
 

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Discussion Starter · #12 ·
(89YT12) this is not a tilt trailer, so trailer-to-bed ground won't be an issue here. But, i have to agree that it almost has to be a ground issue. Now that the trailer has been put back in the out-building, and there's some snow on the ground, and it's turned colder, this project can wait for another day. I agree with you on the proper use of trailer lights. Not having them, besides being illegal (and like you, I'd be the one getting the ticket-not the guy who never uses them) it can be a hazardous situation. Thanks for the input
 

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Just for anyone that stumbles upon this or anyone on this thred but check out ETrailer on you tube they have great videos even for the person who know alot about trailers

http://www.youtube.com/user/etrailertv/featured?ad=5673851196&kw=etrailer&feature=pyv&v=NpVbheV-wTA

they also have a serries "this old trailer" that has some repair and maintance of trailer

http://www.youtube.com/user/etrailertv/search?query=this+old+trailer


and also to you Dave, good luck, keep us posted as you figure out the problem

IDK if you thought of it but check for bare metal where each light bolts to the trailer to be sure the lights are grounding :trink39:
 

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What I do at times to help isolate the problem is take a jumper cable (used for boosting batteries) and connect it to a clean spot on the truck and a clean spot on the trailer. If the lights work then there is a poor connection between truck and trailer. If the lights still do not work, then there is an issue at the lights themselves. Another thing if the problem is at the lights is to take a small jumper and attach it to a good ground and to the base of the socket and see if they work then.

Harold
 
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