T680 Parking Lights

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Vulpine93, Sep 22, 2022.

  1. Vulpine93

    Vulpine93 Bobtail Member

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    Jul 17, 2020
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    I'm trying to track down a problem I'm having where the tractor parking lights/running lights randomly stopped working.

    It started with one of the front peanut (194) bulbs in the left headlight getting very dim then eventually going out completely. Now it seems all of the parking lights (in headlights, tail lights, and on fenders) are doing the same. The trailer parking lights and but trailer and cab clearance lights are working fine as well as the turn signals and brake lights.

    Any suggestions?
     
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  3. Mr Bob

    Mr Bob Light Load Member

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    Mar 17, 2015
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    start checking connections, fuses and relays.
     
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  4. Vulpine93

    Vulpine93 Bobtail Member

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    Jul 17, 2020
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    Fuses and relays are fine, I tried swapping the mirror heat relay and the parking lamp relay with no effect.

    Oddly enough, first the tail lights came back, then the front parking lamps came back as well, but are still flickering and seems to be effected by the turn signals somewhat (they become brighter when the hazards flash).

    I've tried wiggling connections, the wire bundle at the front of the truck, and the switch, nothing seems to effect their operation.
     
  5. Sappy4happy

    Sappy4happy Bobtail Member

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    Apr 23, 2018
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    Have you checked grounding? This type thing is typical of a loose ground connection. The headlights / turn signals seem to be especially prone on the 600 series. Get a tester thing to check for good ground connections and start tracing the wires. I’d start in the obvious spots near the lights where they some times have a ground connection going to the frame. It doesn’t take much to cause problems.
     
  6. Vulpine93

    Vulpine93 Bobtail Member

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    Jul 17, 2020
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    It ended up being the CECU. Man, these Paccar trucks are really crap.
     
  7. AModelCat

    AModelCat Road Train Member

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    131,630
    Jul 7, 2015
    Canuckistan
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    They're all crap.

    The manufacturers all went a step in the wrong direction with multiplexing everything. Stuff was much simpler when they didn't have little boxes everywhere that control everything.
     
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