99 Volvo electrical gremlins - intermittent at first, now here to stay

Discussion in 'Volvo Forum' started by jayfarmlaw, Nov 10, 2023.

  1. jayfarmlaw

    jayfarmlaw Bobtail Member

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    Dec 12, 2020
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    99 Volvo single axle, M11, Super 10, million mile former Fed Ex truck, now farm truck that doesn’t see 10,000 miles a year hauling hay, feed, and equipment.

    Started with right (passenger)headlight staying on while everything off. Turn on the lights on with the switch and back off and headlight went out. I had this problem a couple of years ago and replaced the turn signal switch/cruise and it fixed it, one light would stay on if the high/low switch was not all the way forward. Now, if you turn the left blinker on, the right headlight comes on and stays on. Only way to turn it off is to pull the BATTERY PROTECTION RELAY on the fuse block. With it pulled, lights work normally. All other fuses are good.

    With the headlights on, when you turn on the right blinker, the right headlight seems to partially flash as well. It doesn’t go completely out but dims a little with every blink of the turn signal.

    Today, the ABS light came on. When you turn the left blinker on, the arrow flasher and the ABS light alternate while blinking. Horn was working yesterday, now it’s not.

    Also, the cab side blinker light on the right side does not work at all. Left side normal.

    Any idea where Right headlight circuit, right blinker, ABs light, and horn all come together? What does the Battery Protection relay do?

    thanks in advance for your response.

    Jay
     
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  3. JB7

    JB7 Medium Load Member

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    Dec 13, 2022
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    The Battery Protection Relay is an electronic unit that is designed to protect the batteries by disconnecting uncritical loads when the battery voltage drops below a preset limit.
    "With the headlights on, when you turn on the right blinker, the right headlight seems to partially flash as well." Disconnect the connector at the headlight to check for corrosion and a tight connection. Before reconnecting clean with a cleaner such as Deoxit and use Silicone Dielectric grease. Follow the wiring to check for chafing. Look for a ground wire out of the harness, probably going to the frame, and clean that connection.

    "Also, the cab side blinker light on the right side does not work at all."
    Did you check for power there, did you check the bulb?

    "Started with right (passenger)headlight staying on while everything off. Turn on the lights on with the switch and back off and headlight went out."
    Sounds like the switch. Check for power/voltage at the switch connections with the switch on and off. Is there power going out keeping the light on when the switch is off?
    Really need a wiring diagram as there may be modules involved.
     
  4. DUNE-T

    DUNE-T Road Train Member

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    May 10, 2015
    Detroit, MI
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    Start with replacing ground cables that are attached to frame
     
  5. Vaso.L

    Vaso.L Light Load Member

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    Jan 2, 2014
    South Holland,IL
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    recently had an issue with starter cable that caused the truck to loose all electrical power,everything stopped working except engine.maybe this helps
     
  6. jayfarmlaw

    jayfarmlaw Bobtail Member

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    Dec 12, 2020
    0
    Seems like the problem is in the front right headlight harness. Havent found it yet, but moved some stuff around and problem went away. I’ll chase it further when I have time. Probably run a direct ground from the cab grounds to the battery as well.
    Drive safe!
    Jay
     
    Vaso.L Thanks this.
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