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Trailer light problem

Discussion in 'Mechanic and Repair' started by gogetter, Jan 15, 2004.

  1. gogetter

    gogetter Banned
    Messages: 3,256

    Have a problem with my trailer lights.

    They come on when I brake, use turn signal, and put hazards on, BUT the regular running lights aren't on when I turn the truck lights on.

    What should I be looking at? Thanks.
  2. hole in one lco

    hole in one lco LawnSite Bronze Member
    Messages: 1,793

    1. fuse in your truck
    2. power to the plug
    3. loose wire
  3. tawilson1152

    tawilson1152 LawnSite Member
    Messages: 55

    I presume you mean all your lights come on when you signal, etc. If so, you've got a grounding problem. Most times the ball makes a connection between the truck and trailer, not always. You need a ground wire from your truck frame, through the plug, to the trailer frame. You probably have one that has broken or been corroded. If you have a tilt bed trailer, there should be a ground wire to the frame of the tilt bed also.
  4. grass_cuttin_fool

    grass_cuttin_fool LawnSite Gold Member
    Messages: 3,526

    check and make sure the trailer is grounded good, bad ground accounts for more problems than anything else
  5. gogetter

    gogetter Banned
    Messages: 3,256

    I'm not sure I follow what you mean by "all your lights come on"?.
    Everything seems to work just fine, except the regular running lights (or tail lights, or whatever you call them). The trailers turn signals work, the brake lights work and the hazards work on the trailer. It's just the running lights that don't come on when I turn the lights on at night.

    So with that said, you still say to check the ground?

  6. tawilson1152

    tawilson1152 LawnSite Member
    Messages: 55

    When there is no ground between the truck and trailer, the power to the signal lights will backfeed through the running lights and cause them all to flash slightly. That's one of the most common wiring problems with trailers. I see now that that's not your problem. If you've got a trailer, then you might as well get a 12V tester at the auto store. Trying to troubleshoot without one is just guesswork. Then check to see if you have power at the plug when you turn the lights on. Turn on a signal light at the same time and you can check whether your tester is grounded and working. Depending on whether you have power will tell you where to check next. If your lights on the truck are working, then it's not a fuse. Chances are, it's a bad connection where the plug wiring connects to your truck wiring.
  7. hole in one lco

    hole in one lco LawnSite Bronze Member
    Messages: 1,793

    Your trailer running lites are on a separate fuse. At least mine are.
    Look at your fuse box first be for you start polling wires out .
    Trust me I'm certified in cars electrical systems. 90% of the time its a fuse.
  8. goodbeus

    goodbeus LawnSite Senior Member
    Messages: 392

    put a test light on the truck pigtail...turn your running lights on, and place the test light into each prong...if you get no light out of any prong, the problem is in your truck...check the wire connections and fuse...if you do get a light, then it's your trailer...check the wires, make sure there are no exposed wires and no crossovers...
  9. Premo Services

    Premo Services LawnSite Bronze Member
    Messages: 1,516

    I had that problem also, some lites worked and some didn't.
    I put a new connector plug on the truck and one on the trailer and they are all working fine now. The connectors in the plugs get full of muck and you don't get good connections.
  10. dishboy

    dishboy LawnSite Fanatic
    from zone 6
    Messages: 6,117

    If were talking about tail lights and the truck has them I would first check the wire plug connecter with a 12 volt tester. If I got voltage I would then check the trailer light socket and work back towards the truck until I get voltage. If I get voltage at the plug connector but cant get it any where else I would take a wire with connectors or a jumper cable and ground the trailer to the truck to check. Although if you get brake lights at the trailer but no tail lights I would think your ground was ok.

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