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3 Wires in Trailer Lights - How to hook up

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  • 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
    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!

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    • #3
      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

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      • #4
        Re: 3 Wires in Trailer Lights - How to hook up

        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.
        1998 Wellcraft Eclipse 24 Cuddy
        Volvo Penta Duo-Prop 7.4L "LK"

        2006 Sun Tracker Party Barge 21
        Mercury 90 4-Stroke FI
        "Common sense is not very common"
        "Failing to prepare is preparing to fail." -- John Wooden

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        • #5
          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
          Attached Files
          Last edited by marlboro180; July 14th, 2010, 02:14 AM. Reason: forgot to credit source of image
          A boat is a hole in the water surrounded by wood into which one pours money

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          • #6
            Re: 3 Wires in Trailer Lights - How to hook up

            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?
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            Kevin

            But, where are the reevets?
            1981 Wellcraft V-20 CC Fisherman (FREE BOAT)
            1989 Wellcraft Monte Carlo 28(Build thread here)
            1992 Hotsports Jet'n'Cat Yam 701 WR3 drivetrain "SS George Washington"
            90's Yamaha WRIII and a pair of 95 Kawasaki ZXI-900's
            Fresh clean cheap oil is better then old dirty expensive oil any day
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            • #7
              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.
              1998 Wellcraft Eclipse 24 Cuddy
              Volvo Penta Duo-Prop 7.4L "LK"

              2006 Sun Tracker Party Barge 21
              Mercury 90 4-Stroke FI
              "Common sense is not very common"
              "Failing to prepare is preparing to fail." -- John Wooden

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              • #8
                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.

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                • #9
                  Re: 3 Wires in Trailer Lights - How to hook up

                  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

                  But, where are the reevets?
                  1981 Wellcraft V-20 CC Fisherman (FREE BOAT)
                  1989 Wellcraft Monte Carlo 28(Build thread here)
                  1992 Hotsports Jet'n'Cat Yam 701 WR3 drivetrain "SS George Washington"
                  90's Yamaha WRIII and a pair of 95 Kawasaki ZXI-900's
                  Fresh clean cheap oil is better then old dirty expensive oil any day
                  sigpic

                  Comment



                  • #10
                    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.
                    1998 Wellcraft Eclipse 24 Cuddy
                    Volvo Penta Duo-Prop 7.4L "LK"

                    2006 Sun Tracker Party Barge 21
                    Mercury 90 4-Stroke FI
                    "Common sense is not very common"
                    "Failing to prepare is preparing to fail." -- John Wooden

                    Comment



                    • #11
                      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, 01:18 AM. Reason: Addition to Post.

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                      • #12
                        Re: 3 Wires in Trailer Lights - How to hook up

                        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.

                        1991 Boston Whaler Outrage 17 I
                        2005 Evinrude E-Tec 90hp

                        Fishing isn't a matter of life and death.... It's much more important.

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                        • #13
                          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.
                          1998 Wellcraft Eclipse 24 Cuddy
                          Volvo Penta Duo-Prop 7.4L "LK"

                          2006 Sun Tracker Party Barge 21
                          Mercury 90 4-Stroke FI
                          "Common sense is not very common"
                          "Failing to prepare is preparing to fail." -- John Wooden

                          Comment



                          • #14
                            Re: 3 Wires in Trailer Lights - How to hook up

                            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!

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                            • #15
                              Re: 3 Wires in Trailer Lights - How to hook up

                              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.

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