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  1. #1

    Question Trailer wiring only works with headlights turned off?

    I just bought a jetski and a like new trailer. When I drove away yesterday during the day all lights worked on the trailer; brake, blinker, etc. Well tonight I found that when i turn my headlights on NO lights work on the trailer?? I checked the fuse, trailer ground, and cleaned the connections. So far nothing seems to fix this problem. Anyone ever ran into anything like this before?

  2. #2
    This is why i hate trailer lighting. Do you have another trailer you could plug in and try? Sounds like it could be the wiring on your tow vehicle.

  3. #3
    Click avatar for tech links/info, donation request K447's Avatar
    Join Date
    Jul 2007
    near Toronto, Canada
    The problem is almost certain to involve a poor ground connection somewhere.

    Disconnect the trailer hitch, so the trailer is not touching the tow vehicle (but is right behind it).

    Unplug the trailer plug connector. Now measure the ohms between the exposed ground pin on the VEHICLE connector, and the metal frame of the tow vehicle. Should measure zero ohms, or very close to zero (under 1.0 ohm).

    If that is good, move to the trailer connector. Measure the ohms between the single shrouded pin on the trailer connector and the trailer frame. Should again be zero ohms.

    Also check for corrosion on the pins or socket of the trailer connectors. Corrosion can cause problems. Replace corroded connectors.

    If either measurement shows high resistance (more than 1 ohm), then trace the ground wire until you find the problem. Usually a broken or corroded wire connection.

    If both the above are good ground measurements, then you need to investigate the ground connections at each trailer turn signal lamp.

    Each trailer turn signal lamp must be well grounded to the trailer frame and/or have the ground wire run all the way up to the ground pin on the trailer connector.

    When testing, leave the trailer un-hitched from the tow vehicle, and not touching the tow vehicle. Only connect the trailer plug, and test the trailer lights.

    This prevents the tow ball from acting as an intermittent ground connection between trailer and vehicle. The trailer lights should work perfectly without the trailer being hitched up.

  4. #4
    It's a JEEP thing...You wouldn't Understand dirtdude35's Avatar
    Join Date
    May 2009
    Hurst tx
    do you happen to drive a jeep and are you on jeep forum?

  5. #5
    Moderator DrewNJ's Avatar
    Join Date
    Dec 2005
    Marlton, NJ
    I agree that trailers are just a flat out pain in the ass and that the majority of the lighting problems have to do with a ground. I'd think that if your losing your lights when you turn the headlights on then you have a short in one of the brown wires on the trailer. Probably shorting against the trailer frame...just a guess.

    In all honesty you'll have less time and effort involved in it if you just drop the coin and buy a new light kit and spend an hour or so running some new lights. This way you know everything is the way it should be.
    To many people splice into the light wiring and just flat out do a crappy job that causes problems down the road.
    I don't think I've EVER bought a trailer and not had to replace the lights and wiring....

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