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help with trailer lights?

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  • help with trailer lights?

    I just updated the lights on my tool trailer from older bulb style to led. My signals & brakes work but my. Driving lights don't at all. I tested the connection to the led and I'm getting power. Ok. Its three wires. White-ground. Red-blink&brake. & black-driving lights. I tested red & black by them selfs straight to the battery and they work but when wired on trailer Im not getting my driving lights. Any help is appreciated. Thanks
    Last edited by eecervantes83; 11-27-2012, 07:26 PM.

  • #2
    help with trailer lights?

    green wire- right stop and turning
    yellow wire- left atop and turning
    white wire- ground to trailer
    brown wire- both tail lights, side markers, license plate light, rear marker lights


    • #3
      That's how I have it wired


      • #4
        I think you might have the signals wired to the parking lights and the brakes wired to the brake light. Normally when people go from regular bulbs to LED the complaint is that they can't get the brake and turns to both work.

        The issue stems from LED lights being diodes and only working when the current flows in one direction. The way that normal trailer lights are wired is with the Right Signal and Brake wires going to either side of the bright bulb filament. When the brakes are on the brake wire goes +12V and current flows through the bulb and down the signal wire which is 0V. When the signal is ON the current flows the opposite direction. And when the brake is ON and the turn is ON the bulb goes dark when there is +12V on both wires and bright when the signal is in the off half of the cycle. If you pay attention you will find that when the indicator on the dash is ON the tail light is off when the brakes are ON but they are both on at the same time when the brakes are off.

        To make the LED work the same way you need a diode bridge. The bridge requires 4 diodes for each tail light. It is built by soldering a diode pointing in and another pointing out to both the brake wire and the signal wire. Then solder the two diodes that point out to the LED wire for the bright lights and the two pointing in go to the negative LED wire. Then the parking light wire goes to the LED wire for the dim lights. The parking light will do dark when the flasher is dark and the brakes are on, but that shouldn't be a problem. The parking light will be on an other time.

        You can get the diodes for your bridges at a Radio Shack.


        • #5
          Check your grounds! Ground at the light, ground from trailer to plug, ground from plug to truck. A lot of trailers don't even have the ground wire hooked up, they say it grounds through the metal ball. Put a ohm meter on the rusty ball on a recieve hitch and see how good the ground is. Like Ferbtj said, led's are diodes, power can only go throuh them one way. a regular bulb can have power go either way and when there is a bad ground the power can back feed through the other light and work. Thats why some trailers have brake lights that work until the running lights are turned on then they act up and one or the other work but not both.


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