Tow trailer tail light wiring problem.
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Freshman User
Joined: Sep 2003
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From: Salt Lake City
Tow trailer tail light wiring problem.
I am sure this is a tuff one to figure out due to the vagueness and possibly lack of information, so I apologize in advance. I am setting up a trailer for my 87 Bronco 5.0. I got everything working except the night time break lights. 
When I have my lights on and I then hit the breaks, the lights on the bronco light up but the lights on the trailer go out. Then when I let up they come back on. It is only when I have my tail lights on.
I did not set up the wires from the bronco initially, one of the previous owners did. It has four wires coming from the harness, white, brown, green, and yellow, with the flat four pin connecter.
I am just wondering if there is another wire that has to be included or not included to allow the break lights to work when the tail lights are on. I appreciate any help. Thanks…
When I have my lights on and I then hit the breaks, the lights on the bronco light up but the lights on the trailer go out. Then when I let up they come back on. It is only when I have my tail lights on. I did not set up the wires from the bronco initially, one of the previous owners did. It has four wires coming from the harness, white, brown, green, and yellow, with the flat four pin connecter.
I am just wondering if there is another wire that has to be included or not included to allow the break lights to work when the tail lights are on. I appreciate any help. Thanks…
New User
Joined: Feb 2004
Posts: 2
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From: salem,ohio
on the four wire connector on the trailer, there should be a ground wire! A WHITE WIRE I BELEIVE, Make sure that the trailer lights themselves are properly grounded to the trailer frame . do not count on the tounge & hitch to make a ground. most time a problem with a ground will be light failure - dimming - erratic flashing- wrong signal opperation. hope ths helps & good luck
Posting Guru
Joined: Jun 2002
Posts: 1,028
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From: Panama City, Fl
Sounds to me like a ground problem also. Your brake lights are the same wires as your turn signals. Do the turn signals work properly with the lights on? Try the four way flashers. How do they act? By what you describe, all those functions should effect the tail lights somewhat. White should be ground and the other three are tail, right turn/brake, and left turn/brake. Before believing anyones wire color code, get a meter and check out what is coming out of the truck. Then make sure the trailer is wired to match. I have fixed so many with just a ground set up correct or a couple of wires backwards.
Tuned
Joined: Mar 2004
Posts: 281
Likes: 1
From: Petersburg, MI
Sounds like a ground. When I posted earlier your problem explanation didn't show up just the title(that's why I posted that earler). Make sure the ground wire on the truck is actually hooked up to the frame and the ground wire on the trailer plug ground wire is bolted to the trailer frame. Usually the trailer ground wire isn't hooked up it's just cut off and taped over. If the ground doesn't fix it check all the wiring on the trailer for any cuts/slices. I had a vey similar problem after my wires under the trailer were cut in half by a rock. Spliced them back together and had a prob like you described. It turned out to be the wires behind the pass side trailer tail light. When the wires were cut by the rock they were yanked on some first and this sliced the insulation on the brake light wire(between the trailer frame and taillight assy where it couldn't be seen) so when ever I hit the brakes they all went dim and when I turned on the right turn signal all the lights blinked dim.
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Freshman User
Joined: Sep 2003
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From: Salt Lake City
You guys rule!!! The ground was the problem. I thought I had it grounded correctly, so I changed the location of where it was grounded and made sure it was grounded to the frame, it then started working correctly. I was in the state of thinking I did everything right, and you know what happens when you get in that state. Thanks again.
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