unexplainable electrical problem {lights}

Discussion in 'Freightliner Forum' started by dixieworkx, Aug 10, 2013.

  1. dixieworkx

    dixieworkx Light Load Member

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    heres one for you...2000 freightliner fld-120 classic xl.....ignition switch off, push in the brake pedal or pull the trailer brake lever or '' trolley valve'', the brake lights work fine...problem is that it also turns on every other accessory light, running light, everything but the headlights come on every time i press the brake pedal or trailer brake lever.....

    .so now, if i turn on the ignition switch, every one of these lights come on the minute you turn the key...with the key on, the brake pedal or the trailer brake lever do nothing to the lights, they are all already on, and stay on....

    .if you start the truck with all lights turned off,, all these lights are on, and flicker like the vibration from the truck is shaking shorted wires together...if i turn on the accessory/running lights with the truck running, the lights stay on but the flicker stops.....

    i have shaken every wire, every wire loom, opened the dash, checked everything, nothing seems loose or shorted...short of tracing down every single wire i have done everything possible to find the problem....if i hook up the trailer the problem shows in the trailer also....

    going over the freightliner wiring diagrams i can find no point where the two circuits {brake lights and acc/running lights}intermingle........anyone have any ideas before i go to cutting zip ties and removing wire looms ???????....THANK YOU
     
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  3. IH Truck Guy

    IH Truck Guy Road Train Member

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    If it happens without a trailer hooked up,I would be looking at the wiring going to the tractor tail lites.
     
  4. brian991219

    brian991219 Road Train Member

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    In addition to checking the truck tail light wiring also check inside the tail lights themselves as they can accumulate water and corrosion and short out. I would also check the 7 wire pigtail and the wiring associated with that as the marker/acc lights and brake lights are contained in there as well. s for the lights coming on with the ignition key, that could also be the result of a short in the 7 wire pigtail since there is a 12v feed wire that comes on with the key to feed the trailer abs circuit and it could be shorting out to the running lights. These cords take as lot of abuse and if the plug is coming loose little strands of wire con come out of the back side of the plug and start to short out to other circuits. I would simply unplug the pigtail from the back of the tractor cab (if you can) first, then check for the problem. If it is gone the problem is in the pigtail wiring, if not then check that connect and socket first, working backwards towards the cab and chassis interface. I hope this helps.
     
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  5. Horse Whisperer

    Horse Whisperer Light Load Member

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    Check ALL of your grounds before you go any further... electrical problems are the most costly to diagnose at a shop, usually turns out to be a loose connection or a weak/bad fuse... keep us posted.... Speaking only for myself, I learn an awful LOT on this forum when folks follow up and inform everyone what it turned out to be... thanks in advance.
     
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  6. bigguns

    bigguns Road Train Member

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    Unplug the the trailer power cord from the tractor and see what happens. Remove the rubber boot from the back of the 7 way socket (on the tractor) for the trailer cord to check for corrosion.
     
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  7. 07shaker

    07shaker Light Load Member

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    Its got to be a short that is feeding power to all your other lights through the ground. Do a very close inspection anywhere a wire could be touching any bare metal. Hope you find it; it can be very tough to trace down.
     
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  8. Skunk_Truck_2590

    Skunk_Truck_2590 Road Train Member

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    I bet its either the pigtail or a bad circut/short on the main brake valve body.
     
  9. smf

    smf Bobtail Member

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    Agree with Bigguns above, Check the socket where the pigtail plugs into the tractor. I had a similar problem on mine and it was very corroded inside causing some strange problems with the lights.
     
    Last edited: Aug 10, 2013
  10. luvtotruck

    luvtotruck Road Train Member

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    This forum is awesome! You guys all said what I was also thinking, If you are not addicted to this forum and the plutheria of information that is contained here you will be. Good Luck tracking this down, And like a few others post stated please come back and let us know what you found the problem to be. Thanks.
     
  11. dixieworkx

    dixieworkx Light Load Member

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    i appreciate it people...will start on checking out the above mentioned areas at daylight...started to get on it today but first about 100 degrees here...then rained alot and cooled it down to pleasurable enough to troubleshoot wiring, but i've already got a case of the lazys today :) from sitting around most of it....i have located and fixed many electrical problems but this one really has me lost...of course getting me lost might not be such a hard thing to do now that my sometimers is turning to althetimers haha...
     
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