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Discussion Starter · #1 ·
I hope someone can help out. My trailer lights were acting funny so I replaced the plug end and tail light units. I wired them EXACTLY the same as they were. I hook up to the trailer with my truck, tail lights work but when I turn on the left signal, both lights blink. Right signal, both lights blink. OK I am thinking a short to ground maybe, making both lights blink as one. So I unhook the trailer and use a seperate battery as power source, hook ground to trailer frame. When I hook the hot to each wire they work perfectly. Right light comes on seperate from left, same with left light. I checked all fuses and looked the trailer over, nothing obvious sticks out. Any ideas on what I might try??

Thanks
 

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Contractor
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some vehicles use a connector which has the electrical mechanism that makes the blinkers/brake lights behave properly for trailer use...maybe yours is bad.
 

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Discussion Starter · #3 ·
What part would this be? Is it with the turn signal relay? I will check my other trailer tomorrow and see if it is the same with that trailer. Then I should know it is the truck.
 

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Money Changer
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You have a bad ground on the trailer.

1. You either have a ground wire, under a screw on the trailer that needs to be removed and cleaned.

2. Some trailers need to be hooked to the towing vehicle to obtain a ground thru the hitch and ball contact.

If you have #2, I suggest adding a ground wire to the harness on the trailer side. I had a boat trailer that was wired this way and had the same effect on the signals. Once I added the wire, problem solved.
 

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MOST trailer wiring problems are a result of poor ground like bert already mentioned.

With every trailer we wire we natrually run the grounds from the truck to the tralier through the plugs as they all are, and then i also make a seperate ground wire from the trailer frame and sister that ground up to the inside of the trailer side plug...if that's already in place it may just be a case of having to redo it and make sure you have a good clean grounding surface...but as for grounding, it's impossible to have too many, so if you dont have one, run the seperate/stand alone ground in addition to the grounds going through the plugs.
 

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I had a similar problem 2 years ago when I installed electric brakes on my trailer,
trailer had a flat four, that I had hooked up to my sprinter via a round 7 adapter,
I scrapped the flat four pigtail on the trailer and installed a 7 round pigtail to accomodate the addition of the brakes, that I picked up from the place I got the trailer.
when I hooked up all the colors, brakes worked, lights did as you described, turns out when I looked at the diagram on the plug flap on the tow vehicle, the pin designation to color coding were way off, bottom line, the color coding was not to be trusted, had to refigure what color on the trailer pig tail was what in relation to the truck plug.
don't know if this helps, but it may be a color coding issue???
 

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I had a similar problem 2 years ago when I installed electric brakes on my trailer,
trailer had a flat four, that I had hooked up to my sprinter via a round 7 adapter,
I scrapped the flat four pigtail on the trailer and installed a 7 round pigtail to accomodate the addition of the brakes, that I picked up from the place I got the trailer.
when I hooked up all the colors, brakes worked, lights did as you described, turns out when I looked at the diagram on the plug flap on the tow vehicle, the pin designation to color coding were way off, bottom line, the color coding was not to be trusted, had to refigure what color on the trailer pig tail was what in relation to the truck plug.
don't know if this helps, but it may be a color coding issue???
Nother good point, the RV plugs...7 blade..on the trailer side are color coded completely different than the truck side...Makes no sense to me why the trailer manufacturers were smart enough to make wire color correspond like the truck side does..it makes for a real nightmare when putting new plug end on trailer side.
 

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Head Grunt
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Either bad ground, a bad bulb where one element is touching the other or a bad flasher module. If it is a newer GM truck replace the flasher module.
 

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Discussion Starter · #11 ·
Thanks for all the help, I added a ground wire from plug on trailer to trailer frame, everything works fine now!! It took me 5 minutes to add the wire, I spent 4 hours trying to figure this out earlier in the week. Thanks again.
 

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Thanks for all the help, I added a ground wire from plug on trailer to trailer frame, everything works fine now!! It took me 5 minutes to add the wire, I spent 4 hours trying to figure this out earlier in the week. Thanks again.
:clap: Them GD grounds will kick your AZZZ i tell ya, pulled out many a hair and spent mucho denaro only to find a grounding problem:laughing:
 
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