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Pulsing lights

Discussion in '6.9L IH & 7.3L IDI Diesels' started by Thunderbirb, Oct 28, 2020.

  1. Thunderbirb

    Thunderbirb Registered User

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    New to the forum and new to diesels in general. Bought a 85 Ford F-250 with the stock 6.9. I read a few threads about the pulsing lights. I’ve replaced the alternator and voltage regulator but I’m still getting the pulsing lights at higher rpm but goes away at idle. I’m going to try cleaning off the connects again tomorrow to double check but I find this odd about the situation. When I have the headlights turned on I notice that the engine runs hotter and gets close to overheating and my suspicion is the alternator is generating such a bad parasitic draw that it’s making the engine work harder than it should and heat up. Once I turn the headlights off I can immediately see the engine temp start to creep back down to operating temps. Is this something that anyone has seen with pulsing lights?
     
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  2. IDIBRONCO

    IDIBRONCO IDIBRONCO

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    No. It's probably related tho the dash wiring. There is a voltage regulator behind the dash that the gauge power runs through. The gauges in my Blue Truck will usually read higher with the lights on. I've had other Fords that would vary where the gauges read. Some days higher, some days lower. Your engine probably isn't running any hotter with the lights on than it does with the lights off. The factory gauges in these trucks are next to useless. They aren't even close to being accurate. They are basically an idiot light with a moving needle and are mostly to make the driver feel good. A good set of aftermarket gauges is the only way to get accurate information on how your engine's running.
    As for your pulsing lights, that's a new one on me. I've had two different Dent Side trucks (1973-1979) that had lights that would pulse slightly at an idle, but not an higher RPM. One stopped doing it after I put another alternator on it. The other one, my last one, a 1979 F150, did it no matter what. I guess it just liked to pulse the lights at an idle.
     
  3. IDIBRONCO

    IDIBRONCO IDIBRONCO

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    By the way, welcome.
     
  4. Thunderbirb

    Thunderbirb Registered User

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    My wiring behind my dash is kind of messed up from the previous owner cutting and splicing wires so it wouldn’t surprise me if the wiring is the problem. Even if the gauges are dummy lights I will watch the voltage gauge on the cluster and it will bounce up and down. The batteries are charging which is the most important thing to me but it just worried me watching the temp gauge go up when I’m driving at night with the lights on. I’ll Have to invent in some better gauges and try that.
     
  5. Thunderbirb

    Thunderbirb Registered User

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    I posted a video to YouTube to show what exactly the truck is doing
     
  6. chillman88

    chillman88 Supporting Member Supporting Member

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    Does it do it all the time or just for a minute after starting the truck? Both of mine will do that for a little bit immediately after starting while the glow plugs cycle themselves a few times. Might be a different issue especially with yours being an 85, but figured I might as well mention it just in case.

    How long have you had the truck? Is this a new issue or has it always done it?
     
  7. IDIBRONCO

    IDIBRONCO IDIBRONCO

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    On your truck, it's actually an ammeter. It has a "D" on one side and a "C" on the other. I've only had one truck where the needle on the ammeter actually moved. Of course that changed when I did the 3G swap with my Blue Truck. The needle will move quite a bit when I start it now.
     
  8. Thunderbirb

    Thunderbirb Registered User

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    It will do it all the time. I can watch the lights pulse while driving to work in the morning. I never noticed the issue until I started driving when it dark. During the daytime I don’t see any issue. As one person said, the amp meter on the dash will still bounce up and down as I drive even during the daytime but I don’t see anything wrong. Then when it’s dark I get a good view of the pulsing lights. I’ve read a thread that said everything goes through the headlight switch so I thought maybe the headlight switch is going bad but I’m not really sure.
     
  9. chillman88

    chillman88 Supporting Member Supporting Member

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    http://www.garysgaragemahal.com/icvr.html

    That's what he's talking about. Good information to know whether it ends up being your issue or not.
     
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  10. chillman88

    chillman88 Supporting Member Supporting Member

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    It is odd to see the headlights doing it too. I'm wondering if you have a bad ground somewhere? How do your battery cables look? I'd inspect the grounds on the body near the lights too.
     
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  11. Thunderbirb

    Thunderbirb Registered User

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    I suspected a bad ground so I ran a test today to check if that could be the issue. I connected the jumper cables up , one clamp to the body of the truck and the other end directly to the negative on the primary battery but even doing that I still saw the lights do the same thing. The lights did brighten up when I connected it that way so I’m sure I can improve the grounding. I’ve even tried mismatching where I connected the engine directly to the negative terminal but didn’t see any change. So I’m pretty positive that’s it’s not a ground issue. I’m going to try to use the regulator behind the dash and see if that works
     
  12. Thunderbirb

    Thunderbirb Registered User

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    I’m definitely going to try this. It couldn’t hurt to do this. I’m still going to get some new gauges later but this is great info to know! Ill do it tomorrow and see what happens!
     
  13. snicklas

    snicklas 6.0 and Loving It!! Staff Member

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    One thing to look at. On our 83 F-150 351, our lights flashed like that. What we found was on the passenger side, by the battery there was a little rectangular box, about the size of a piece of Trident gum. Has 2 studs. We found the connections to it were bad. Put new ends on it and it quit flashing. Sorry I don’t have better info, but this was almost 30 years ago.... LOL
     
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  14. Selahdoor

    Selahdoor How can I help you, or make you laugh, today? Supporting Member

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    I am wondering if your glow plugs are cycling when the lights are pulsing...
     
  15. franklin2

    franklin2 Full Access Member

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    I think it's still a grounding issue. The cluster is not grounded properly, that is the reason you think it's getting hotter when it's really not. The cluster needs to be grounded, the cab needs to be grounded and the front sheetmetal needs to be grounded. The factory had a ground strap from the rear of the engine to the firewall. There is another grounding point for most of the truck behind the radio up high on the inside of the firewall. I would just run a short ground from the radiator support to the negative cable for the frontend.

    I was working on a very rusty truck, and I ended up having to ground the alternator with a extra wire. It should be grounded through the brackets, but they were so rusty and they were all frozen.
     
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