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Flickering interior lights and low indicated voltage on dash only 200 1993

posted by  drj434343 on  Mon Dec 16 14:31 CST 2019
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last visit: Thu Oct 24 09:46 CST 2013
[RELATED]

On my 93 240 wagon, I have a long standing issue of apparent low voltage and electrical load sensitivity on interior circuits only. This issue worsens as the car gets fully warmed up. The symptoms are:

1. Dash mounted VDO voltmeter drops to 12-13 V after starting at 14-15 V.
2. Dash light brightness flickers randomly, and dims notably when a high load accessory like the blower motor, wiper blades, or turn signals actuate. I also see extreme dash voltmeter jumps downward when large accessories are used.

Generally, as loads increase (headlights, foglights, etc), the voltmeter drops to 12 V or sub-12 V levels. Levels that would make you think you weren't properly charging the battery.

When this issue occurs, I can put a calibrated voltmeter directly on the battery terminals and read 13.8 - 14 V steady. The voltage fluctuations in the cabin appear to be independent of the true charging voltage on the battery (engine running).

I was running a 100A Bosch alternator, but as a sanity check, I installed a Denso 100A unit and got the same results. Steady charging voltages at the battery, but low voltage and load sensitivity inside the cabin.

I'm thinking this looks like a bad or partially bad ground somewhere. Is there a ground tree located somewhere that could cause this issue just on interior circuits, but leave the primary charging circuit alone?








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    Flickering interior lights and low indicated voltage on dash only 200 1993

    posted by  machine man on  Mon Dec 16 17:33 CST 2019
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    last visit: Wed Oct 22 15:40 CST 2014
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    Hi,

    There two ground points off of the battery. One goes to the body of the car and the other directly onto the engine block.
    I would definitely check into the body ground cables on the battery and get the area under the body a good work over.

    When we go over to look at the positive side to view things.
    Breaks in conduction from either side + or - acts the same way and so far you haven’t mentioned particular switches only just the loading of various circuits.
    If the main cable work correctly, it would seem to be a distribution issue.

    We have to start with the small red wire on the battery post. It can become lame with corrosion very easily as it can be under the wires insulation and within the ring terminal crimping.
    That little wire goes over to a terminal block on the fender that’s full of spade connectors that also feed various circuits depending on accessories.

    The main fuse panel is the next place to investigate.
    The panel is in the cabin “drivers door” hinge area and is the next stop. Some of its power comes from that outside connections box near the battery.
    Take all the fuses out of there and give them a good cleaning of the tips. Replace those that look corroded across the face or the tip are flaky. If any are loose and tighten up the brass fingers holding the fuses by squeezing them lightly if needed.

    I spray down the whole assembly down with a very light coating of corrosion inhibitor to ward off moisture vapors that come from the drivers floorboard during rain and snow seasons.
    The door jam is a cold source area and when moisture vapors are warmer in the cabin they will migrate to any colder area.
    Proof of this happens all the time right in front of our eyes when the glass in the car gets foggy.
    The metal of the whole car does the same thing, just out of sight and out of mind!

    I don’t if anyone ever thought about rain or just water!
    Imagine if it had a color, any color and if if stuck to every thing, like it does.
    What a mess that would be! Good ole’ White Snow is bad enough, just because it clumps up!

    This all should be a good start towards eliminating these worrisome issues.

    Phil







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      Flickering interior lights and low indicated voltage on dash only 200 1993

      posted by  drj434343 on  Wed Dec 20 09:56 CST 2023
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      last visit: Thu Oct 24 09:46 CST 2013
      [RELATED]

      I realize I never responded to this post but did end up finding the problem.

      The main 12V wire that goes from the alternator underneath the crank pulley and connects to the starter had an intermittent connection right under the crank pulley where the wire harness is essentially clipped to the block.

      The harness in this location had grown very stiff with age, and resistance measurements across this run of wire varied wildly when the car was hot and the engine was running (vibrating).

      I'm not sure if it was corrosion, fatigue, or a combination of both that did it, but there was a heat and vibration dependent partial break which resulted in large resistance swings. This wreaked havoc on all the 12V systems when the car was hot.

      Replacement of this run of 12V wire completely eliminated the issues.








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        Flickering interior lights and low indicated voltage on dash only 200 1993

        posted by  machine man on  Wed Dec 20 12:43 CST 2023
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        last visit: Wed Oct 22 15:40 CST 2014
        [RELATED]

        Hi,

        Thanks for the feedback!

        That problem you found was a big one all right. That would have turned into some smoke of melting plastic.

        Glad to see you found it and are on top of keeping the car running.
        Our cars are get more rare by the day.
        Luckily wire is going to bet around for a long time to come!
        If you need more the new cars are putting more and more batteries into the trunk areas. That’s a long run back to the front. Imagine that!

        Guess we have been receiving a training process, all along, to be ready for electric vehicles.
        But watch to see how stupid or hard the access to them we be let alone any power connectors that are barely standardized.

        I’m wishing for hydrogen fuel cells like the rest of the globe is moving towards.
        Hydrogen is everywhere on the planet and safer to transport than gasoline. Sky tankers are in the works.
        Read up on it.
        Meanwhile save the planet from making more of what it doesn’t need. Old simpler cars are an easier medium to live with for now.
        IMHO.

        Phil







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        Flickering interior lights and low indicated voltage on dash only 200 1993

        posted by  machine man on  Wed Dec 20 11:13 CST 2023
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        last visit: Wed Oct 22 15:40 CST 2014
        [RELATED]

        Hi,

        The interior items are fed current directly from the battery positive post by a separate smaller wire.
        There could be corrosion or frayed ends under the terminals. Mostly off the big cable end.
        That wire goes over to a little black box on the fender well.
        Just because it looks small doesn’t mean it can’t be a bigger thing.


        When you have a voltage reading across the battery you only get the battery voltage.
        Your problem lies down the line. This can happen on either side of a circuit or circuits in this case the head of the snake can mostly like be a battery connection to the terminal block or the tabs there and any associated wiring.

        I already told you about the big cables.
        If you are having so many different problems you need to start from the supply side and work outward.
        The next place is the fuse panel in the front door hinge area.
        A problematic area due to its a cold place that draws moisture to it.

        It doesn’t help that the fuse holders lose tension either and combined with corrosion on the tips it become a one by one chase unless you clean them all. I keep some very light spray every couple of years on mine but the I keep my cars inside a lot or living in California helps with less humidity.

        If you are lucky in some respects, that the problem are where I suggested it be, then you have a fix at HAND 🤭 and some light work.

        Phil







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