Lights won’t turn off

Discussion in 'Volvo Forum' started by Paul Chamberlin, Oct 30, 2020.

  1. Paul Chamberlin

    Paul Chamberlin Bobtail Member

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    Hey guys, anyone have this issue??
    Lights come on and flashers quit. Headlights not fog lights on, 4 way and signals don’t work marker lights on truck and trailer (driver side only) come on and won’t go off with all off on the switch. I keep having to unplug the batteries to turn them off (probably a computer issue). Ive had a few different trailers and same issue. Most likely a wire somewhere messing with the computer. Any ideas or knowledge on where to look would be helpful.

    2015 vln 780 with electric idlefree apu.
     
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  3. Paul Chamberlin

    Paul Chamberlin Bobtail Member

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    When parked they turn themselves on!! Grrr what the hell!!!
     
  4. FLHT

    FLHT Light Load Member

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  5. Paul Chamberlin

    Paul Chamberlin Bobtail Member

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    Got to be an open circuit somewhere, possibly water in it. Not sure where to look tho.
     
  6. OldRed98

    OldRed98 Light Load Member

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    I hate electrical issues. and It only gets harder with newer trucks. There are a bunch of sites online now that have PDF manuals you can pay to download. I would see if I could download schematics for those circuits and start tracing the lines. I'm friends with the parts people at Kenworth... They printed my electical schematics for my jakes when I had issues. I found the prior owner of my truck spliced a dash fan into any hot wire he would find... Just so happend to be my Jake switch.

    I recently had an ECU on my Dodge go bad. Sent it off to a place called ECU exchange and they repaired the circuits for me. They only charge like $75 to check out an ECU and $250 to repair but took them about a week with mailing it in. Not sure if they do big trucks.
     
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  7. Paul Chamberlin

    Paul Chamberlin Bobtail Member

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    Some of the wiring for the electric APU looks sketchy in the fuse box, ( tapped into existing fuses) I’ll start there then go fishing to see if I cans find any breaks or bad connectors. So far it’s only happened while I’ve been parked, hoping it doesn’t happen while I’m driving as it affects turn signals.
     
  8. lilillill

    lilillill Sarcasm... it's not just for breakfast

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    Turn off the battery disconnect switch. Unbolt the bulkhead wiring connector on the firewall, spray the connectors with silicone spray and then plug it back in.

    Turn the master switch back on and report back.

    It could be the Lighting Control Module (under the fuse panel) but I doubt it.
     
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  9. 6cuda6

    6cuda6 Light Load Member

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    Also visually check the light harness that runs along the hood including connectors...look for stuff that doesnt appear similar to the rest or corrosion in connectors...ive seen lots of them corroded/damaged from rubbing on hoof hinges etc
     
    Paul Chamberlin Thanks this.
  10. 6cuda6

    6cuda6 Light Load Member

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    Everyone needs to remenber something....volvo switches all circuits to ground....which means there is always power being fed to components so when you flick a switch it completes the circuit with a ground.

    So your lights are shorting to ground (chassis etc)....thats why they are on.
     
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  11. Paul Chamberlin

    Paul Chamberlin Bobtail Member

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    Yep completely re-wired that over the summer also did tail lights harness. I see 2 connections under the bunk that will be where I look next.
     
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