1. Can’t make it to the GIE+EXPO 2017?
    LawnSite brings the trade show floor to your fingertips with our new GIE+EXPO 2017 Sneak Peek video series debuting now in the Lawn Mowing forum.

    Dismiss Notice

light problem on trailer

Discussion in 'Trucks and Trailers' started by mike lane lawn care, May 15, 2006.

  1. mike lane lawn care

    mike lane lawn care LawnSite Bronze Member
    Messages: 1,707

    ok so the right tail light on the trailer stays on all the time, even when the truck is turned off, sometimes it works but not often, the truck is a Jeep grand cherokee, with aftermarket towing and lighting setup. all other lights work, we just replaced the plug on the truck and the problem still persistes, there is the same problem on 4 trailers that we have tried, so it isn't the trailer. What the heck is going on?

  2. stuffdeer

    stuffdeer LawnSite Bronze Member
    Messages: 1,617

    Check the grounding of the wires.
  3. mike lane lawn care

    mike lane lawn care LawnSite Bronze Member
    Messages: 1,707

    how would i go about that? i don't have a huge mechanical ability but with enough instruction i can figure it out. thanks
  4. LindblomRJ

    LindblomRJ LawnSite Silver Member
    Messages: 2,570

    The ground is generally the white wire in the light harness. Is the aftermarket light harness one that plugs into the tail light harness of the tow vehicle? If so it is the white wire needs to have contact with the frame or metal body part.
  5. oldrustycars

    oldrustycars LawnSite Senior Member
    Messages: 301

    are you saying that one light stays on with the lights on the tow vehicle turned off? just one right tail light? and the same on 4 different trailers? first off, are you certain it isnt the brake/turn signal thats on? did this trailer ever work correctly?
    trailer lights are simple, they dont have to be a nightmare that they often turn into. as has been stated, CHECK THE GROUND. thats usually the first place to look, but i dont think thats your trouble. you need a 12 volt test light. without one, dont bother going any farther. they're less than 10 bucks. with the trailer unplugged, and the tow vehicle lights off, check to see if power is anywhere in the plug. is the plug a flat 4, or a bargeman RV style? your jeep may have a factory towing package that often has 12 volts hot line to power lights or a fridge in a camper. it could be frayed and contacting the right turn signal wire. i dont think you have the right taillight on because the tail and running lights would all be on the same circuit. in any case, get the info we need and post back, or PM me, i'll be happy to help.
  6. scholzee

    scholzee LawnSite Member
    from NY
    Messages: 130

    The Jeep Grand Cherokee without a tow package cannot have trailer wiring hooked up without a special adapter, the factory wiring without the trailer package is not heavy enough Gage to drive the truck lights and trailer lights. The adapter has a heavy Gage wire direct to the battery and is hooked to the factory wires just to turn on an internal relay or electronic switch, the switch in the adapter is most likely stuck on, or water and corrosion got in the case causing the light to stay on. Follow the wiring back to you get to the module, unhook the +12 volt supply from the module and in the light goes out the module is bad. Also try here for more info http://www.jeepsunlimited.com/forums/forumdisplay.php?f=51
  7. scholzee

    scholzee LawnSite Member
    from NY
    Messages: 130

    What is a ModuLite, ModuLite Lite And ModuLite HD?
    A ModuLite is a trailer light power supply module which provides power to the trailer lights directly from the tow vehicle's battery. By powering the trailer lights in this manner, the tow vehicle's tail, turn and stop light circuits are not exposed to any additional loads.

    Why Is This Important?
    In many cases the tail, turn and stop light circuits of today's vehicles are connected with light gauge wire, designed only to carry enough current to supply the lights the vehicle is equipped with. Additionally, some vehicles are equipped with sensitive electronic devices, such as "lamp-out" sensors, which are designed to monitor the vehicle's electrical system and warn the driver of problems with that system.

    The additional load of trailer lights on these devices can cause them to react falsely and in some cases may lead to their failure.

    Which Vehicles Need A ModuLite?

    Is the vehicle equipped with any option packages that include a lamp-out sensor or other electronic devices that could be damaged by attaching trailer lights directly to the vehicle's electrical system? If so, a ModuLite is required.

    Is the trailer being towed equipped with more that one light assembly per side? Does it have clearance lights, dual tail, turn or stop lights or any other equipment that will impose an extra load? If so, a ModuLite is required.

    Is this the only trailer the driver will ever tow? Consider future requirements as well as current ones. In future applications, a ModuLite may be required.

    Are There Other Ways To Determine The Need For A ModuLite?
    Yes. Vehicle manufacturers caution consumers against adding additional loads to electrical circuits. Consult the vehicle owner's manual when recommending trailer wiring. The following are two examples from owner's manuals:

    Jeep Grand Cherokee
    "Do not connect a trailer lighting system directly to the lighting system of your vehicle. Use an approved trailer wiring harness. Failure to do so could damage the vehicle electrical system and/or result in personal injury."
  8. mike lane lawn care

    mike lane lawn care LawnSite Bronze Member
    Messages: 1,707

    it is the flat 4 plug style, i checked it and the plug on the Jeep with the green wire has power and is keeping only one tail light on, with that light, the blinker does not work, it is just a steady light. the problem is definately not the trailer, we have tried several trailers and they work on other trucks just not on ours.
  9. mike lane lawn care

    mike lane lawn care LawnSite Bronze Member
    Messages: 1,707

    i don't belive that the wiring is directly connected to the other lights, in the fse box there is a fuse for "trailer tow", and harness looks like it was professionaly installed. the wiring comes out into the cargo area of the jeep and then we run it through the back liftgate to get to the trailer. The Jeep was previously used to tow a 5,000 lb. camper and a 5,500 lb. Boat
  10. scholzee

    scholzee LawnSite Member
    from NY
    Messages: 130

    Green is right turn / brake, follow the wiring back and see if it goes to a module, something is keeping it on. What year is the Grand Cherokee ?

Share This Page