Kenworth T600 trailer brake light issue

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by caribou8820, May 23, 2020.

  1. caribou8820

    caribou8820 Bobtail Member

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    Jan 21, 2014
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    Lost the brake lights the other day. They work on the tractor but not the trailer, same on multiple trailers so in the truck; but that's as far as I got. Are the trailer brake lights going to be on a separate circuit?
    It's a 99 T600, guess I'll have to start at the trailer connector and work from there. Just a shot in the dark to see if someone can point me where to start looking. Can't see anything obvious in the wiring, but it has been messed with right in front of the 7 pin connector with some splices; so that is a little suspect.
     
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  3. TankerYankr

    TankerYankr Medium Load Member

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    First check the circuit at the end of your pig tail, then unplug the pig tail from the tractor side and check the circuit as it comes from the tractor. That will narrow it down to if it's in the pig tail or the tractor.
     
  4. AModelCat

    AModelCat Road Train Member

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    First thing to do is check the fuse. Any short in any trailer you've hooked to could have popped it.
     
  5. caribou8820

    caribou8820 Bobtail Member

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    The brake light fuse I found was good, unless there is a separate one for the trailer I missed?
     
  6. Deattris1985

    Deattris1985 Bobtail Member

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    Dec 27, 2019
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    Question are the marker lights working on the trailer? If so check the wiring in the rear of the trailer for any broken wires for the brake lights. Than I would check for current coming to the brake lights on the trailer. If no current and no broken wires go to your 7way plug coming from the truck and check for current there. If you have current coming from the truck. Next check the 7way plug that plugs into the trailer for current. If you don't have current than you need to replace the the 7way plug. If you have current than check the plug it self on the trailer for corroded wires.
     
  7. caribou8820

    caribou8820 Bobtail Member

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    Found the problem, Wire was broke going to alternator, so was not powering trailer relays.
     
  8. AModelCat

    AModelCat Road Train Member

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    I've been wrong before but I've been turning wrenches for over a decade and that doesn't sound right. I think it may have been a coincidence. If it is, good chance the problem is somewhere near the area you found the broken alternator wire.
     
  9. caribou8820

    caribou8820 Bobtail Member

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    Jan 21, 2014
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    Well, just to double check. Disconnect the wire, about 10 gauge; no trailer brakes, but still tractor.
    Hook back up trailer and tractor. I traced the wire, it goes up to the back of the engine, front of the firewall; brings power to the trailer brake relays and I don't know what else, seems like that is the main purpose of it. It looks original; not added on or anything.
     
  10. AModelCat

    AModelCat Road Train Member

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    Ok perhaps that's where KW decided to take the 12 volt power feed for the T600 then. Never seen that before.
     
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