Thread: trailer lights

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  1. 08-01-2018, 02:10 PM #1
    gip50
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    USA trailer lights

    ok guys having trouble with my trailer lights. a friend left the boat ramp right behind me the other night and informed me i had 1 brake light and 1 turn signal. could not get them to work so went and bought 2 new tail lights thinking that would solve problem. did not. I have the green going to green and the yellow going to yellow and the brown/green and the brown/yellow going to the brown on the 4 wire flat plug. Running lights are fine. left side turn and brake lights are fine. right side is not. when i step on brakes right side gets dimmer. when i hit left turn signal both sides blink. when i hit right turn signal nothing blinks. not sure if its ground issue or wiring issue. traced right side lights all the way back and did not see anything wrong really don't know where to go from here. Any help on what/where to look now would be great. Thanks
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  2. CatFan
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    #2 08-01-2018, 02:12 PM
    Check the fuse in your tow vehicle. There is a separate one for trailer left and right sides for brake/turn, then one for trailer running lights and one for trailer backup lights on most vehicles.
    If you have integrity, nothing else matters. If you don't have integrity,
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  3. Team Dougherty
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    #3 08-01-2018, 02:19 PM
    From the symptoms you are describing I would say you have a bad ground. Make sure the white wire is grounded to the trailer and on the Tow vehicle. Make sure the studs on the taillights are touching metal and not paint. If the taillights have a white wire connect it to the trailer frame.

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  4. fishnfireman
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    #4 08-01-2018, 02:37 PM
    ^^^^ bad ground would be my first thought also.
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  5. scubatelco
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    #5 08-01-2018, 02:59 PM
    I had a bad pin connection in the 7 pin to 4 pin adapter on my truck.


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  6. Jonestrollingmotor
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    #6 08-01-2018, 03:14 PM
    Sounds like a bad ground to me also. As stated above, make sure all the ground connections are clean and properly grounding through the plug -- not through the trailer ball.
    If your truck has separate fuses for trailer left brake/turn and trailer right brake/turn, that is an easy check.
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  7. gip50
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    #7 08-01-2018, 05:42 PM
    have checked fuses in truck. were not bad. changed 7 pin connector out, didn't help. changed 4 pin out, didn't help. everything works now but right side brake light and turn signal. I have left turn signal and left brake light, but when left turn signal is on every light on trailer blinks. when right signal is on right side on trailer blinks, but can barely tell it. no brake light no matter what on right. Have everything working, but right side. Beginning to think might be plug-in on truck even though put on a few months ago. hooked to my friends truck and had brake lights and turn signals working, but no running lights. He had no hitch so probable wasn't grounded which caused no running lights. again just a guess. As far as i can tell ground is solid. took it loose and cleaned and put back on wasn't any difference. Have tried everything suggested so far and so far no luck. really frustrating.
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  8. CatFan
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    #8 08-01-2018, 06:32 PM
    Look at the ground at the lights. Should be a white wire to trailer frame at every light.

    The hitch has has nothing to do with the ground
    If you have integrity, nothing else matters. If you don't have integrity,
    nothing else matters.​
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  9. fishnfireman
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    #9 08-01-2018, 07:57 PM
    If there is no white wire at the light. Some are made to ground through one of the mounting bolts.
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  10. billnorman1
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    #10 08-02-2018, 07:32 AM
    These guys are trying to tell you you have a bad ground on your truck or trailer. On the wiring harness there is a white wire. It must go to a clean bare metal part of your trailer. It must also go to a reliable ground on your truck.
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  11. Team Dougherty
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    #11 08-02-2018, 09:38 AM
    delete
    Last edited by Team Dougherty; 08-02-2018 at 09:54 AM.
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  12. gip50
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    #12 08-02-2018, 09:38 AM
    replaced ground wire no difference. Have found out if not on hitch no running lights. put on hitch running lights raised and running lights quit as soon as quit making contact. plug on truck bumper is only 2 months old. tried different 7 pin and 4 pin, no difference. again thinking something in tow vehicle? Ideas? advice? had problem? Believe i have tried everything suggested so far. just about ready to give up.
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  13. Team Dougherty
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    #13 08-02-2018, 09:53 AM
    Quote Originally Posted by gip50 View Post
    replaced ground wire no difference. Have found out if not on hitch no running lights. put on hitch running lights raised and running lights quit as soon as quit making contact. plug on truck bumper is only 2 months old. tried different 7 pin and 4 pin, no difference. again thinking something in tow vehicle? Ideas? advice? had problem? Believe i have tried everything suggested so far. just about ready to give up.
    That is a bad ground. All lights should work with trailer off of ball. Check tow vehicle ground and trailer ground. 95% of all trailer light problems are ground related. replacing the wire will make no difference if it is not grounded properly.
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  14. billnorman1
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    #14 08-02-2018, 11:56 AM
    Looking into the 7 pin plug on the truck you must have ground on the socket at approximately the 7:30 position.
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  15. Jonestrollingmotor
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    #15 08-02-2018, 01:54 PM
    As others have tried to say -- it is a bad ground. If the lights do not work with it off the ball, then you are relying on the hitch to make the ground connection which is a bad idea. The white wire coming from the 4 or 5 wire flat (if that is what is plugging into the 7pin must be carrying a ground. The other end of that wire will be grounded to a solid clean place on the trailer.
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  16. Team Dougherty
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    #16 08-02-2018, 02:21 PM
    Quote Originally Posted by Jonestrollingmotor View Post
    As others have tried to say -- it is a bad ground. If the lights do not work with it off the ball, then you are relying on the hitch to make the ground connection which is a bad idea. The white wire coming from the 4 or 5 wire flat (if that is what is plugging into the 7pin must be carrying a ground. The other end of that wire will be grounded to a solid clean place on the trailer.
    Also look at the ground side of the tow vehicle. Make sure the white wire from the plug is going to a ground on the Tow vehicle.
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  17. mikeky
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    #17 08-02-2018, 03:36 PM
    If you have a swingaway tongue make sure ground wire is connected to trailer after it.
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  18. ncredbear
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    #18 08-02-2018, 04:41 PM
    If you just recently replaced the 7 pin plug on your truck my guess is that I where the problem is. Either you hooked the ground white wire to the wrong pin or in working on it you pulled the other end of the ground wire loose. This is on your truck not your trailer.
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  19. billnorman1
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    #19 08-02-2018, 06:02 PM
    If you replaced the 7 pin plug on your truck, the wires coming off the back of that plug going to your vehicle do not necessarily match up to the same color wires on the trailer harness. I straightened one out last month for a guy, the wires on the back of the 7 pin truck connector definitely did not go yellow to yellow, white to white etc.
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  20. gip50
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    #20 08-03-2018, 08:41 AM
    thanks guys, found out plug did not align with truck. Had to buy different type plug-in and started working correctly.Appreciate all the help. Always know where to go for anything boat related.
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