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Thread: Trailer lights question? Anybody? HELP!

  1. #1
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    Default Trailer lights question? Anybody? HELP!

    Ok,
    Trailer wiring issue.
    1. All new wires/lights on the entire thing.
    2. Wire harness is continuous 20 foot run to back of trailer. Only
    splice is at the lights themselves.
    3. Ground wire is sanded clean times 2, dielectric grease applied.
    Screw tight.
    4. hooked up, Drivers light is fine. side indicator lights fine.
    Passenger tail only works with the brakes when the lights are OFF. No
    turn signal, no lights when they are turned on. Shut off lights, hit
    brakes, then they work.
    5. Take tester with ground wire (20 feet connected directly to harness)
    and test wire. Have lights/power down entire length of trailer. Now, in
    the roller guides, I loose ground/connection somehow. Might be the
    attachment or whatever, but I loose the light in the tester.
    6. The repair. Take wire off tester, place directly on screw of
    passenger light, viola!!! I have lights.
    7. NEW PROBLEM.....
    8. lights, passenger seems pretty darn bright compared to driver, like
    someone is standing on break. NO blinker when lights are on. NO brake
    lights when lights are on. Shut lights off, blinker and brakes both
    work......
    9. Help?


  2. #2
    Join Date
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    Default

    Sounds like:
    1 - ground issues, run a ground wire all the way to the plug. Don't rely upon the frame.

    2 - brake (turn) and tail light wires (passenger) are touching somewhere. possibly corrosion along the line, plug etc.

    brake and turn are the same circuit. Tail is separate.

    1 - brake and turn (right)
    2 - brake and turn (left)
    3 - tail
    4 - ground

  3. #3
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    May 2003
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    cosby tenn
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    My ranger truck had the same problem early in the summer.I had to buy a new plug assembly to plug into the truck wiring.It seems the wires from the truck that plugs into the boat wiring has some sort of deal in it that seperates the power and puts it where its supposed to be.The wire run under my truck was bad in that section.Once I replaced that part it works fine now.The plug in I'm talking about has a "black box" attached to it that you cant get into, you have to replace the whole thing.Works fine now.

  4. #4
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    Default

    Quote Originally Posted by geeman
    My ranger truck had the same problem early in the summer.I had to buy a new plug assembly to plug into the truck wiring.It seems the wires from the truck that plugs into the boat wiring has some sort of deal in it that seperates the power and puts it where its supposed to be.The wire run under my truck was bad in that section.Once I replaced that part it works fine now.The plug in I'm talking about has a "black box" attached to it that you cant get into, you have to replace the whole thing.Works fine now.
    I forgot about the newer rigs requiring the wiring adapter. Good point!

  5. #5
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    cosby tenn
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    YA thats the phrase I was looking for ! Wiring ADAPTER! My memory fails me since the stroke ,sometimes I cant bring the "data" up like I would like to.

  6. #6
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    I had checked and double checked every wire , plug, everything I could think of. It all went back to the truck I couldnt find any problem with the trailer harness.Then I remembered the harness under the truck,replaced the under truck harness WITH the RIGHT harness for THAT truck and problem solved

  7. #7
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    North Sydney, NS
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    Default lights

    eric, I had the same problem on my old trailer, twice. Turns out the first time, somehow someone jammed to bulb in wrong, which is a three pole bulb. There are two poles on the bottom of the bulb, and the base of the bulb is the ground. Because of this ground hadn't changed, but the voltage coming from the tailights of the truck was going into the wrong pole, in this case to the element ment to show brakes or turn indicators, which coincedentally is a brighter element. The voltage from the turn signals/ brakes, meant to go to the brighter of the two elements in the trailer bulb is now going to the dimmer fo the two. Think of it like trying to see the light from a lighter that someone is holding in front of a flood light, all you can see is the brighter of the two, turn off the bright one, and there is the lighter. That is why you can't see the turn/ brake light while the vehicle headlights are on. Switch the wires, or check the bulb to make sure it is in the keyway for proper alignment. That is my guess. I bet that even though you turn signal/ brake work, with headlights off, they are dimmer than the side working properly. Second time I had the problem, I forgot to say, was that the wires had been swtiched to make up for the problem that was caused with the bulb installed backwards a second time! rather the put the bulb in right.

    Good luck.

  8. #8
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    I repplied to late! either way as long as it works!

  9. #9
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    No i didn't.............. that wasn't you, ok time to get away from this thing for a bit.

  10. #10
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    Thanks for the responses.

    I have separate ground wires run all the way back to the harness at the front. These are completely new wires/lights and there are no splices except right at the lights which are mounted to the roller guides.

    CBKyle, I did take the light apart, twice actually, played with the bulb, no difference. I will try to rewire the light to see (just for fun I guess) You seem to describe is well with the spotlight/lighter deal. Just driving me crazy since it is all new, and separate gounds run from each light and NOT to the frame....damn, thought that would have cured it, but NOPE, new problem....

    Any other thoughts? Oh, vehicle plug is brand new as well and the tester shows it is fine and it works on my other 4 trailers just fine.....

  11. #11
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    Apr 2003
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    San Juans, WA
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    Some random ideas, and I wonder if you have more then one issue here...

    1) Assuming that any conversion from separate brake and turn lights which your truck may (or may not) have has been taken care in the trucks wiring harness. Given that you can make other trailers work, sounds like it has and that means you have 4 wires between the truck and the trailer to worry about: Ground, Running Lights, Left Turn+Brake, Right Turn+Brake.

    2) Make sure the truck is good. Some of this sounds like grounding problems, and the ground issue might be in the trucks socket wiring. At times a bad ground can be masked through the trailer hitch. I would use a testerlight directly on the trucks socket. And use the sockets ground pin, not the truck frame. Make sure all 3 other wires mentioned above work like they should.

    3) Make sure the trailer lights are wired correctly. Even if new, there might have been a manufacturing error where you get say the running light wire crossed with a brake light... You talk about a splice at the roller guides, could this be a source of crossed wires?

    4) Make sure the ground wire (Good you run back a wire all the way, not relying on the trailer chassis) makes good contact with the light bulb sockets. Esp with the tail lights a bad ground can cause all sorts of funny issues.

    My guess: Reading above I think you have grounding issues back to one, or perhaps both, of the tail lights. After geting that fixed, there MIGHT be a crossed wires at one of the tail lights. But I would start with the grounds.

    Hope this helps.
    -al-

  12. #12
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    Use a volt ohm meter and check for voltage drop. If you are using ribbon cable make sure there are no kinks. Quite possible you might have a wire broken in the insulation. It happens when pulling wire.
    Also take a long wire and use as a jumper to ring out the harness.
    Use the ohm setting on the meter for this with no voltage applied.
    If the harness checks out you most likely have a shorted light housing. You can check that to the same way.

  13. #13
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    Well until your reply eric I was gonna say the fancy adaptor thingy because I had the exact same problem with a BRANDY NEW adaptor. The giveaway though was that I had the same faulty lighting issue in each of three trailers.

    Still, it could be in the pluggy thing on the trailer end--they are made incredibly cheaply and it is not at all hard to envision a short or fault in the plugtowire connections. It should also be easy and cheap to replace.

  14. #14
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    Default dielectric greese

    dielectric greese is non conductive, will seal out water and O2, but will isolate terminals, this may or may not be your problem. Just my personal experience with dielectric greese. If you have a 7 way plug on your truck there are 2 types, center aux and center brake. The center AUX is called southern wiring. Center brake northern wiring. reguardless of vehicle make. This may have no use to you but I feel beter getting it off my chest Good luck

  15. #15
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    oops grease

  16. #16
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    I had a similar problem earlier this summer. I hooked up new lights to the trailer got nothing. I drove myself crazy trying to fix it. I rewired the trailer several times and tested the truck. I eventually just exchanged the lights for the same set, and that solved my problem. I don't know if this helps, but it worked for me.

  17. #17
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    God knows why, but I dont think any of the vehicles sold in NZ ( I may be wrong - a "new" vehicle isnt even a blip on my personal radar) have a place to plug in a special harness/adapter for a trailer plug - the plug is either part of the loom or itsnot catered for at all.

    The common approach here is to hack into the wiring loom where it enters the tail lights and pick up the connections to the trailer plug that way - so you know they are right!!
    Nobody I know of uses the trailer chassis as an earth return, especially not on boat trailers where the lights and licence plate are often on a "light board" that gets hung on the transom of the boat. Obviously this has no connection to the trailer at all - it is a great way of keeping the lights out of the water as long as you remember to remove the board from the boat before you go down the ramp. Also a great way of moving the licence from one trailer to another. Yep. :-)

    Pete

  18. #18
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    Smile Whoa !!!!

    [QUOTE=Eric D][SIZE=1]Ok,
    Trailer wiring issue.
    1. All new wires/lights on the entire thing.
    2. Wire harness is continuous 20 foot run to back of trailer. Only
    splice is at the lights......................
    [QUOTE]

    Hold on.
    You need to be able to use a multi tester to know what is going on so you don't have so much trial and error. You can't see electrons,you can only measure them.

    First We have the issue of the trailer lights then a seperate issue is the vehicle lights.

    First lets start with the trailer lights.
    With your multimeter You need to know which wire from the taillight is the ground. Set the meter on the ohms scale. Is the light plastic or metal? Check the wires to find ground by connecting one lead to the light housing then the other test lead to one of the wires from the tail light.

    Once you know which is the ground wire and if the tail light assy is grounded to the frame the you can find out what the function of the other wires is. Sometimes the package instructions are wrong. Hard to believe but true. take two long 14 gauge wires and hook them to a battery . One to ground. One to +. Then touch each wire of the tail light with the positive wire to find out which i one lights up. That will be the regular taillight. The wire that you touch with the brake pedal depressed and the ignition key on IS THE BRAKE LIGHT Mark them and label them.

    The next thing to do is to establish those same facts with the vehicle wiring. Some vehicles come with a pigtail of wires to be used for trailer wiring. If you can find them. Otherwise you will need to SPLICE into the car wires to get the three wires for the trailer.

    1.GROUND
    2. 12 volts for regular tail lights (12 volts when light switch is ON)
    3. The wire coming from the vehicle brake light switch for the brake lights which will have 12 volts ONLY when you depress the brake pedal with the ignition key on.

    Hope this helps.
    Last edited by donald branscom; 10-06-2006 at 01:41 AM.
    I love the smell of fresh cut plywood in the morning.

  19. #19
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    Thanks to all who replied. I will go through the mental gymnastics (or masterbation as some call it...) this weekend when I launch the boat and get it off the trailer which will make putzing with the wires easier. I have printed all of this off and will attempt a remedy. \


    Thanks again.

  20. #20
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    I had a similar problem this summer. I bought a boat in New Hampshire and had to get it to Conn. Of course, the lights didn't work on the trailer. Worked on them for about 4 hours. Finally someone suggested that I go to the local camping supply store and buy a set of "clamp on's". Did so, for 20 bucks, clamped them on the boat and drove home. A lot easier, and they will fit on any and all trailers that I want to haul.

    Kevin G
    \"Of all the things I\'ve lost, I miss my mind the most.\"

  21. #21
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    Also a great way of moving the licence from one trailer to another. Yep. :-)

    Pete[/quote]

    Great idea, epoxybuoy! I never thought of that. No more failed wofs!

  22. #22
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    Quote Originally Posted by Caleb Chia
    Also a great way of moving the licence from one trailer to another. Yep. :-)

    Pete
    Great idea, epoxybuoy! I never thought of that. No more failed wofs![/QUOTE]


    Yeah, but at some point you do need to front up with ONE good trailer !!!

    Pete

  23. #23
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    Eric, The problems that you discribed in your original post are common when trying to operate trailer style (one 2 filiment bulb per side) from a tow vehicle with seperate rear turn signals.
    Light adapters convert the electrical signals into what the trailer system needs. Depending on your tow vehicle, several types of "adapters" are available. Many late model vehicles have lighting systems controled by a computer, this requires an adapter that is self powered directly from the battery to avoid toasting the computer. Vehicles with any sort of "bulb check" system would also need this type of adapter.

    Lots of good info is out there for just this kind of problem. Look at the "towing" and "tow vehicle" forums on this RV site.
    http://www.rv.net/forum/index.cfm

    This one will tell you if you need an adapter.
    http://www.trailerwiring.com/cgi-bin/main.cgi

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