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Trailer Wiring Problem... Please Help.

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  • Trailer Wiring Problem... Please Help.

    I have looked at the other trailer wiring posts and didn't find the same problem I am having. This might get a little long, please bear with me:My tow vehicle is a 98 Toyota 4-Runner with separate turn signal and break lights. I had the correct splitter installed professionally. The plug is the flat, 4-wire type - white, brown, green, & yellow.I have tested the vehicle side with a tester and all seems to be in correct working order. I bought a new wire set for my trailer. It has the flat connector but it has 5 wires - white, brown & green, green, brown & yellow, and yellow.Using a new brake light/turn signal with 3 wires - white, black, & red, I can get only the running lights to work when hooked up correctly or the turn signal light will burn constantly but brighter. I am positive I have a good ground all around. Basically what I get is running lights only - no brake lights or turn signals. It is also this way with the old wiring.I greatly appreciate any and all responses to this problem!!Thanks in advance...Russell


  • #2
    Re: Trailer Wiring Problem... Please Help.

    Russell,THe "Fifth" wire is used for a surge brake lockout on disc brake trailers for backing. It is tied into the back up light circuit of the tow vehicle. I think you can still use it.I do not know the layout of the five wire flat plug you have. Basically, you want to do tie the following circuits together.1. White-Ground2. Brown-Running3. Green-Turn/Stop4. Yellow-Turn/Stop

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    • #3
      Re: Trailer Wiring Problem... Please Help.

      DJ,I understand the wiring sequence you described but the connector splits the turn signals into the brown/green and brown/yellow wires.One other thought I had but forgot to mention earlier: Could the problem be in my flasher? I have heard that sometimes a flasher might not be powerful enough to handle a trailer's wiring.Thanks.

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      • #4
        Re: Trailer Wiring Problem... Please Help.

        Hi Russell Take a test light or voltmeter and check each wire going to the trailer. They should function as follows:yellow = left turn and brakegreen = right turn and brakebrown/green = marker lights for right sidebrown/yellow = marker lights for left sidewhite = groundIf the above wires do what they should when each function is energized, the problem is probably in the connections from the trailer harness to the left and right lights on the trailer. The lights have three wires going to them. As you say....white, red, black. Take the lens off and look to see which wire goes to the bulb ground (socket). That will be your ground. That wire should go to the white wire in the harness and/or to trailer frame. The other two wires hook to brake/signal and marker. I 'll bet that its these two wires you have mixed up, resulting in the vehicle marker lights powering the trailer brake/signal lights. The brake/signal filament is much brighter than the marker filament so even when you step on the brake, or use the signals, the incorrectly wired marker circuit drowns out any added light.good luck!
        Alias "schematic"

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        • #5
          Re: Trailer Wiring Problem... Please Help.

          hi, i'm having a very similar problem with my 89 4 runner except my trailer only has two wires for each light; red and black. My wiring harness from my truck is a flat 4 prong, as is the harness I connected to the trailer. I get all sorts of weird stuff goin on when I do different things in my truck. If I leave my running lights off, everything seems to work. I turn my lights on and my turn signals turn into hazard blinkers and my brake lights don't work. I also don't have running lights at all on my trailer. I only have three wires coming from the tongue of my trailer so I have the ground tied to a bolt. What can I do to make it all work. that's all I want.thanx

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          • #6
            Re: Trailer Wiring Problem... Please Help.

            hi glastron brian Does your vehicle function normal when the trailer is NOT connected?Do you have a testlight or voltmeter?Have you checked the function of each wire at the plug?Yellow = left turn and brake lightGreen = right turn and brake lightBrown = marker lightsWhite = groundOnce you have tested the vehicle, we'll move on to the trailer......
            Alias "schematic"

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            • #7
              Re: Trailer Wiring Problem... Please Help.

              schematic,my truck lights all work fine. I'm home today working on the thing, and I just noticed that the harnes from my truck has green, green, yellow and white wires. Weird. Also my trailer only has green, red and brown and black wires.

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              • #8
                Re: Trailer Wiring Problem... Please Help.

                oh, and I do have a voltmeter, but i don't know how to use it very well. any help there would be great. I am a complete and total novice...as if it isn't obvious

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                • #9
                  Re: Trailer Wiring Problem... Please Help.

                  okay, I fixed the trailer lights. Everything works like it should. I had to rewire the whole thing, but at least it works. I didn't have a good ground and only taking a blind chance let me to find the proper ground....BUT...now my brake lights in my truck and therefore the trailer won't come one. what's up with that? Even if I disconnect the trailer they don't work on my truck.

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                  • #10
                    Re: Trailer Wiring Problem... Please Help.

                    check the fuses in the truck......(drivers side under the dash) If fuses are OK, check the bulbs. Did you know the cruise won't work in your toyota if the brake lite bulbs are burnt?
                    Alias "schematic"

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                    • #11
                      Re: Trailer Wiring Problem... Please Help.

                      schematic, i just wanted to say... what?!!!!you mean the cruise takes a signal off the brake circuit, and requires the filaments in the bulbs to be intact?!! as in a specific V, instead of doing something simple, like having the cruise input with its own grnd.... i have a toyota- that bites

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                      • #12
                        Re: Trailer Wiring Problem... Please Help.

                        ebbtide176Its the way they monitor the brakes. If the ECM sees a ground, it engages cruise. If it sees anything other than a ground, it won't. Just think of it as a poor mans bulb monitor. If I remember right, it won't engage if the brake fluid is low either!
                        Alias "schematic"

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                        • #13
                          Re: Trailer Wiring Problem... Please Help.

                          Alias "schematic"

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                          • #14
                            Re: Trailer Wiring Problem... Please Help.

                            Hi RussellYour car wiring is as follows (as also stated by DJohns and Schematic);White = GroundBrown = Tail/Running LightsGreen = Right Turn And Brake LightYellow = Left Turn and Brake Light(Note: this is not NZ style, as I suggested in the other trailer wiring post. We have a seperate brake circuit ).Your trailer (new wiring set) is;White = GroundGreen = Right Turn And Brake LightYellow = Left Turn and Brake LightNow as for the brown/green and brown/yellow - I agree with Schematic - you should tie these to the brown wire on your car because they are the tail/running lights.

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                            • #15
                              Re: Trailer Wiring Problem... Please Help.

                              Thanks, I will check it out and see if that works.

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