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  1. #1
    Petty Officer 2nd Class
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    Default 3 Wires in Trailer Lights - How to hook up

    I've got an old trailer that I bought that the wires on it have been spliced in a number of places but the tail lights work well. So I thought for preventative maintenance, I would replace all of the wiring. I bought a standard 25' of four wire with a flat four wire flat connector. I just noticed that each of the tail lights have 3 wires coming out of them, a red, white and black.

    I know that the green is the right turn, yellow is the left turn and the brown is the tail. What is the correct way to hook up this up to the red, white and black coming out of the existing lights?

    Thanks for your help.

  2. #2
    Lieutenant Commander Rocky_Road's Avatar
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    Default Re: 3 Wires in Trailer Lights - How to hook up

    Strange color coding at the lights!

    If I had to wager, I would assume that black is your running light, red is your stop and turn light, and white would be your ground.

    Let us know!

  3. #3
    Admiral j_martin's Avatar
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    Default Re: 3 Wires in Trailer Lights - How to hook up

    You'll have to test one of them. White is ground (neutral) in ac electrics, but usually in automotive you'll find the black is ground. There is no standard that I know of.

    You can do it with an ohmmeter. From the frame of the light, (or the base of the bulb for a plastic one) ground would be zero ohms or close. The next higher reading would be the turn/brake light. The highest resistance would be the tail light.

    hope it helps
    John

  4. #4
    Supreme Mariner bruceb58's Avatar
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    Default Re: 3 Wires in Trailer Lights - How to hook up

    Quote Originally Posted by j_martin View Post
    You can do it with an ohmmeter. From the frame of the light, (or the base of the bulb for a plastic one) ground would be zero ohms or close. The next higher reading would be the turn/brake light. The highest resistance would be the tail light.

    hope it helps
    John
    Both filaments are going to measure 0 ohms so you can't do it that way. Just hook it up to a battery and see which wire has the brightest light which is your brake.
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  5. #5
    Lieutenant Junior Grade marlboro180's Avatar
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    Default Re: 3 Wires in Trailer Lights - How to hook up

    White is most likely to be yer ground, but check that first as people do funny things to wiring, and also since it was spliced together.. The diagram below is how the wires should go , but test your existing lights first to see whats what.. Are these original lights or replacements?

    http://www.easternmarine.com/em_stor...ight_tech.html
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    Last edited by marlboro180; July 14th, 2010 at 02:14 AM. Reason: forgot to credit source of image
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  6. #6
    Admiral smokeonthewater's Avatar
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    Default Re: 3 Wires in Trailer Lights - How to hook up

    Quote Originally Posted by bruceb58 View Post
    Both filaments are going to measure 0 ohms so you can't do it that way. Just hook it up to a battery and see which wire has the brightest light which is your brake.
    Where the heck do you come up with this stuff?
    bulb1.jpgbulb2.jpg
    Kevin

    Quote Originally Posted by Tinnie
    But, where are the reevets?
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  7. #7
    Supreme Mariner bruceb58's Avatar
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    Default Re: 3 Wires in Trailer Lights - How to hook up

    You are correct. I was wrong about this. Got 0.3 ohm on one filament and 2.0 on the other.

    The problem is that just a little resistance can throw the measurement off. For example...just putting both leads on the bulb base will yield up to 0.6 ohms just from the resistance of the contacts.
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  8. #8
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    Default Re: 3 Wires in Trailer Lights - How to hook up

    Marlboro, I've got a stupid question for you. In your wiring diagram, it shows the brown wire going down both the driver and passenger side of the trailer. I was just going to continue the wire from the first light across the back of the trailer to the second light. Otherwise I would need an additional brown wire, right?

    Also, I was going to do the same for the ground wire on the lights. That is run a wire from the ground on the first light over to the second light and then ground both of them near the second light. If I do it that way, I'm going to have to join three of the wires together. What's the best way to make a good waterproof three wire connection?

    Thanks again.

  9. #9
    Admiral smokeonthewater's Avatar
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    Default Re: 3 Wires in Trailer Lights - How to hook up

    Quote Originally Posted by bruceb58 View Post
    just putting both leads on the bulb base will yield up to 0.6 ohms just from the resistance of the contacts.
    I got 0.0 there... I suspect your meter needs calibrated
    Kevin

    Quote Originally Posted by Tinnie
    But, where are the reevets?
    1981 Wellcraft V-20 CC Fisherman (FREE BOAT)
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  10. #10
    Supreme Mariner bruceb58's Avatar
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    Default Re: 3 Wires in Trailer Lights - How to hook up

    Judging from the look of your meter, I am sure 0.0 is well within its tolerance rating.
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  11. #11
    Seaman Apprentice Hawk Eyes's Avatar
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    Default Re: 3 Wires in Trailer Lights - How to hook up

    Yes that wiring will work. For example; if you run your wiring down the right side of your trailer, you can then run your yellow, brown spliced, and white sliced wire across the back rail to your left light and tap in your rear marker lights as well.
    Last edited by Hawk Eyes; July 15th, 2010 at 01:18 AM. Reason: Addition to Post.

  12. #12
    Lieutenant saumon's Avatar
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    Default Re: 3 Wires in Trailer Lights - How to hook up

    Quote Originally Posted by Hawk Eyes View Post
    Yes that wiring will work. For example; if you run your wiring down the right side of your trailer, you can then run your yellow, brown spliced, and white sliced wire across the back rail to your left light and tap in your rear marker lights as well.
    It will work, but you're better to do it well right now if you rewire. Splice right at the tongue. That way, if you get a chafed wire somewhere, you won't loose all your lights. And an even better practice is to run separate ground wire up to the tail lights instead of relying only on the frame.

    As for the splices and any connections, solder then heat shrink tubing is the way to go.

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  13. #13
    Supreme Mariner bruceb58's Avatar
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    Default Re: 3 Wires in Trailer Lights - How to hook up

    Most premade trailer wiring run kits have the running lights go down both sides of the trailer but your method will work as well.

    As far as running a seperate ground, that is really unecessary. Make sure every light has a good clean fastening point to the frame and you will be fine. If you rely on a seperate ground wire, you just added a complete new path to troubleshoot when the light doesn't work.
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  14. #14
    Lieutenant Commander Rocky_Road's Avatar
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    Default Re: 3 Wires in Trailer Lights - How to hook up

    Quote Originally Posted by saumon View Post
    It will work, but you're better to do it well right now if you rewire. Splice right at the tongue. That way, if you get a chafed wire somewhere, you won't loose all your lights. And an even better practice is to run separate ground wire up to the tail lights instead of relying only on the frame.

    As for the splices and any connections, solder then heat shrink tubing is the way to go.
    You can run seperate brown wires down both sides of the trailer, but if any part of the brown 'chaffs' and shorts you will still blow the fuse...and lose all of your running lights. In theory the less the length of the brown wire, the less the chance of having a short.

    It is true that if you run the brown down both sides...and one side simply has a poor connection...you will keep the one good side lit. That is a good reason to run both sides!

    Happy boating!

  15. #15
    Seaman Apprentice Hawk Eyes's Avatar
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    Default Re: 3 Wires in Trailer Lights - How to hook up

    Quote Originally Posted by saumon View Post
    As for the splices and any connections, solder then heat shrink tubing is the way to go.
    No better way to make a connection than the above statement.

  16. #16
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    Default Re: 3 Wires in Trailer Lights - How to hook up

    Very cool. Thanks for all of the help.

    And by the way, if this helps anyone else, stop and turn is the black wire, tail light is the red and ground is the white.

  17. #17
    Supreme Mariner bruceb58's Avatar
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    Default Re: 3 Wires in Trailer Lights - How to hook up

    You positive about that? Sure you aren't turning on both filaments when putting votage between white and red?
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  18. #18
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    Default Re: 3 Wires in Trailer Lights - How to hook up

    When I pulled out the assembly, on the back of it, that's how it was marked. You're probably right though. I tried a number of different combinations and came to the conclusion that I had a bad bulb in one of the lights. I was going to replace the bulb but the unit was sealed. So I checked on a replacement light and with shipping, it was around $25 so I went to plan B.

    Plan B was buy a $28 trailer kit and replace everything which I did. LOL!

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