Trailer light wiring colors

Discussion in 'Wiring' started by Kelby Bullard, Nov 27, 2017.

  1. Kelby Bullard

    Kelby Bullard New Member

    Nov 27, 2017
    61A7E915-BF5B-4FAD-8352-8D1B256AD537.jpeg 4C2629B5-D899-47DB-A19C-132938E2FB3D.jpeg I have a 1975 Bethany compact 560 and the plug was cut off prior to my ownership. The 5 wires for the plug are completely different from the color wires going to the lights. A five wire cable runs through the walls and the lights splice off of that one cable. But I can’t tell what color goes to what light. I have tried applying voltage to each wire individually to see what lit up but only two worked and both lit up the markers and tail lights.
  2. NMroamer

    NMroamer Active Member

    Apr 21, 2016
    Albuquerque NM
    Wish I had an easy answer for you but there isn't one.
    Track and check connections one wire at a time to see where it goes. Changing wire color doubles the work.
    Good luck! Patience.
  3. NMroamer

    NMroamer Active Member

    Apr 21, 2016
    Albuquerque NM
    After thought but I would not count on it. White is negative or ground and brown is running lights.
  4. roybraddy

    roybraddy Well-Known Member

    Mar 23, 2016
    King George, Virginia
    I think it will be be pretty good saying WHITE is FRAME GROUND and BLACK is AUX +12V on the newer trailers.

    But your trailer being as old as it is they may still be using RED as +12v and BLACK as -12V Automotive wiring colors...

    Using a multimeter ($15 WALMART-LOWES) put one lead on frame ground of the truck and then use the other lead to measure 12VDC as you walk through the functions STOP LIGHTS-RUNNING LIGHTS-LEFT and RIGHT LIGHTS etc...

    My truck has the drawing of the 4-way and 7-way receptacle with what each pin or blade is for on the outside lid cover...

    GO TO and look at all of their trailer wiring diagrams posted there.

    Be careful just shorting this to that when connected up to the truck - you will blow some fuses which may be hard to find. ON my truck they are all fused lines and I believe they are located behind the passenger side kick panel inside the truck.

    For just testing which lights come on the trailer on each of those wires you are showing I would use an outside source of 12VDC - Not the truck. Then you won't blow any hidden fuses inside the truck.

    I have one of those JUMP START units like this one that helps out big time doing something like this...

    Roy Ken
  5. michaeltdyer

    michaeltdyer Member

    Nov 26, 2012
    Denver Colorado
    You need to get an Ohm Meter and a log piece of wire and trace out the wiring. If your trailer has a battery, always disconnect that first. Then use the Ohm Meter to determine which wire goes to what. I presume this trailer does not have electric brakes, so you should have the following connections:

    Ground - test this simply by putting one meter lead on the metal and probe each wire
    Aux 12 volt - test this by putting one lead on the + 12V connector on the batter hookup or if you have the cigarette lighter socket, check to the center connection inside the socket
    Backup Lights - test this from the light socket
    Left Turn / Brake light - test this from the light socket
    Right Turn / Brake light - test this from the light socket

    Once you figure out which wire controls what, you just have to buy a plug and hook it up! Good luck!

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