Engine dies when the headlights are turned on

Discussion in 'Technical' started by Tumbler, Mar 6, 2021.

  1. Tumbler

    Tumbler Member

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    My car suddenly developed this problem where every time I turn on the headlights the engine dies. If I pull the light switch out part way to turn on just the tail and signal lights, the engine starts stumbling and running rough. When I pull the switch out all the way the headlights flicker for a few seconds before the engine dies. I'm not sure about this, but for the bit of time they're on with the engine running, the headlights seem brighter than usual. When the engine is off, they are clearly dimmer than usual.

    The battery voltage is 12.6. It's 14.3 when the car is running, so it seems like that should be fine. I'm not sure if it could somehow be related, but I managed to drain the battery a few days ago. I accidentally left the ignition switch on. It doesn't need the key in it to turn. It drained the battery down to 8 volts. Jumping it wasn't enough, so I had to pull out the battery and put it on the charger.
     
  2. Krazy Comet

    Krazy Comet Tom

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    Sounds like the alt is under charging at idle. Erratic running, stumbling etc with lights on are almost sure signs of low voltage.

    Time to check battery voltage when idling with lights on...
     
  3. Tumbler

    Tumbler Member

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    I did some more checking, and the battery goes to 11.8 with the lights on when the car is off. Today the headlights aren't killing the engine, but it still runs rough. When it's running with the lights on, the voltage is at 13.
     
  4. maverick7072

    maverick7072 Member

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    krazy comet do u think the alt. could be my problem?
     
  5. Krazy Comet

    Krazy Comet Tom

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    Voltage should more like 14.4, at least 13.8...
     
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  6. maverick7072

    maverick7072 Member

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    i was running my heater and headlights when my car shut down, not sure if i hit my brake pedal or not when it shut down, but everytime i started it back it would die when i tapped the brakes so i unhooked the brake switch just so it would stay running and i could get it home ,
     
  7. Tumbler

    Tumbler Member

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    I got a bit more time to mess around with this. It's giving me the impression that something's loose or shorting out. There will be periods of time when the headlights are totally fine, but then they'll to start to flicker and glitch out again. The engine will run rough and/or cut out occasionally. The passenger side headlight wants to go dim or turn off. Sometimes they both turn off, and I can get them on again by pushing the switch in and out a bit. With the headlights off no problems are apparent.

    I wonder if it has something to do with the headlight switch? I though I heard crackling coming from it at one point. Electrical problems are my least favorite thing try and deal with. Instead of having straight forward symptoms, everything just sort of goes insane.
     
  8. Krazy Comet

    Krazy Comet Tom

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    The HL switch controls both R&L, if only one is acting up 100% different problems. If both go wonky, yes could be switch.
     
  9. Constable

    Constable You have the right to remain silent....or not!

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    The switch is the most likely culprit. Still, checking the wiring is a prudent thing to do also. I wouldn't think that the switch malfunctioning would affect charging voltage that much, if at all. It would have to be one helluva short. One thing about the stock alternators you need to understand is that they are very restricted to charging voltage. I found this out back when I did my police car resto and using the extra emergency lights pulled the voltage down to nothing. These stock alternators put out just enough volts/amps at idle to run the car minimally. Doesn't matter what factory options it has like a/c as they only used one alternator. As the alternator ramps up at speeds, it puts out more but just enough to properly charge the battery with accessories on like lights, heater, etc. If memory serves, they are made to only put out something like 60-80 amps at max output which would be around at least 40mph. If everything electrically is up to snuff and the battery is in good shape, the only way that the car would suffer is if it was left idling for a long time with everything on under normal circumstances.

    One other thing to consider with undercharging is they have a three wire configuration as to charging system. That means that the external voltage regulator could also potentially be at fault.

    How I fixed my past undercharging issue was to get a custom alternator with the same size case as the stock one and converted it to a modern one wire. It was a simple conversion. This upgrade allowed me to go to a 120 amp alternator which improved not only the operation of accessories, but the ignition system always got the proper voltage. People forget that if the ignition system doesn't get the proper voltage, it won't operate efficiently.
     
  10. Krazy Comet

    Krazy Comet Tom

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    Orig units of '60s/'70s were sized according to accessories. Without air, 42A were most common though I've seen 38A as well. AC or HD system received 55A.

    Orig 1970s #6014 lamp low beam draw 3.91A each, high 4.69A. Modern halogen #6024 draw 2.73A low(so much for halogens drawing higher current) & high same as orig 6014. It's the heater blower that is most hungry, can draw 15-20A on high.
     
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  11. Tumbler

    Tumbler Member

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    I think I came across a clue as to what might of happened. The Honda I used to try and jump the Maverick has suddenly come down with electrical problems. The engine won't turn over, and every time I try the dash lights flicker. I'm wondering if I may have hooked up the jumper cables backwards. This seems like too much of a coincidence, otherwise.

    I'll have to go through the relays and fuses tomorrow. A while back the Honda needed a jump, and my friend hooked up the cables backwards before I could warn him. All it did was kill a relay.
     
  12. Tumbler

    Tumbler Member

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    I went and replaced the voltage regulator. I was trying the replace parts until the problem is solved approach, and the voltage regulator is easier to replace than the headlight switch. So far everything seems to be working normally. The headlights and dash lights are brighter than they were before.
     
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