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  1. #1

    Default No low beams but all four lights work on high beams

    I have an 83 gt and one night my battery died and then i had no low beams anymore. I turn my high beams on and I have all 4 lights working. I've bought a new multi function switch, pull out switch to on and off, voltage regulator. All motocraft parts with no change in the symptoms. Any help is greatly appreciated.

  2. #2

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    I am not trying to be a smart a$$. Did you check that the sealed beams are good?

    I would check that the is power for the low beams at the headlight plug. You didn’t mention this in your post.

  3. #3

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    I was looking for a wiring diagram for both switches but I can't find any. I only assumed it was good because all four headlights turn on with high beams. I'm still looking for diagrams On the forum. I'm not very good with electrical yet learning all of this as parts break. In college currently for automotive tech.
    Last edited by Stangsgt83; 05-20-2018 at 06:29 PM. Reason: Needed more background

  4. #4

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    Check the pigtails on low and on high. Confirm you have power there. Then work it back from there. There is a sticky with all the wiring diagrams.

    Also, this would be a good time for the headlight relay upgrade and/or led light conversion.

    Although I am not an auto tech, l know a bit about electrical.

  5. #5
    FEP Supporter 4-barrel Mike's Avatar
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    From the 1985 EVTM (Electrical & Vacuum Troubleshooting Manual). 1983 should be the same

    You should get an 83 for your car https://www.ebay.com/itm/1983-Mustan...kAAOSwEA9a30op absolutely worth the money.

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  6. #6

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    Thank you for all of the great info. I'm going to dig into my car tomorrow. I don't have my test light at home and I'll keep u updated. Very respectfully Chad.

  7. #7

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    I just place my order for that manual. Thanks again. I can't wait to be able to drive my car on the daily again

  8. #8

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    I started having the same problem with my 83 last fall Don't drive it much but I'd like to see the outcome of your problem

  9. #9
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    For reference the year by year electrical schematics are in a sticky in the Electrical section. As noted, the lighting wiring should be close between the models and years with the exception of driving lights added.

    I would do as above and start at the sockets to see if you have power for the lows and work back from there. Seems the dash switches can cause issues over time but not sure if that would cause your particular problem.

    Good luck!

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  10. #10
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    The are two different headlights in your car. One is a high beam only and it is a single filament type. The other one is a two filament type. One filament is for low beam and the other is for high beam. So when you turn on high beams, both lights are lit on high. When low beam is on, then only the low beam filament is use in the dual filament bulb. So if both low beams are out, then you may just have both bulbs blown in the duel filament bulbs.

  11. #11
    FEP Member brianj's Avatar
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    Quote Originally Posted by dynodon64 View Post
    The are two different headlights in your car. One is a high beam only and it is a single filament type. The other one is a two filament type. One filament is for low beam and the other is for high beam. So when you turn on high beams, both lights are lit on high. When low beam is on, then only the low beam filament is use in the dual filament bulb. So if both low beams are out, then you may just have both bulbs blown in the duel filament bulbs.
    This. Check the sockets for power first. Before you think that can't happen, I lost all 4 bulbs in a '68 roadrunner, one after the other, in the course of 15 minutes one night. Once the power draw of two bulbs is cut down and all circut power available is sent to one bulb, if the remaining bulb is weak, it will pop too.
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  12. #12

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    I'm curious to what your problem ended up being, if you solved it yet. I have had the WORST luck with my lights in my 85. After losing my low beams I did the relay upgrade. It solved my problem. Then one night I lost lows and highs. That was scary on a dark road in the middle of nowhere. One of my wires I ran for power for my relays fell onto my header (my fault of course). A month later a relay went bad. I was fine for a little over a year up until a couple months ago. Kept losing my lows again. All wirings, grounds, and switches were fine. The cheap set of HIDs I bought went bad on BOTH sides at the same time. My highs still worked. I junked the outer HIDs and stuck some silverstar ultras in there for the time being. They were still fine when I parked the car 5 weeks ago to do my 347 swap. Knowing my luck the lights are gonna give me issues again shortly after I'm done lol

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