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    dimming lights

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    scy135
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    dimming lights

    Post  scy135 on Thu May 07, 2015 12:22 am

    Ok so when I drive my 78 wagon I noticed all my lights dim when I drive they kinda light back up again when I brake or come to a stop. To me it kinda seems like an alternator issue. Also my engine kinda feels like its misfiring or something its also really lacking in power lately. Just wanted to get a second opinion or some advice.
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    Re: dimming lights

    Post  GM B-Body Forum on Thu May 07, 2015 10:39 am

    Sounds like an alternator, you can get those tested at any auto parts stores on or off the car, so id get it checked out. As far as power, that could be from the alternator, when it dies off the car is just running on the battery and the hei needs at least 12.6 volts to run correctly, so it could cause misfiring.


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    Re: dimming lights

    Post  scy135 on Thu May 07, 2015 12:02 pm

    Ohh ok right on I had a feeling it was the alternator. Thanks alot buddy!
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    Re: dimming lights

    Post  scy135 on Wed May 13, 2015 1:01 am

    i just got my alternator tested and its running perfectly fine. my lights dim and come on bright randomly what could be the problem?
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    Re: dimming lights

    Post  GM B-Body Forum on Wed May 13, 2015 12:05 pm

    Have you checked all the wires and connections and made sure your getting a good ground? run the car without the alternator connected and see if it still does it, then disconnect the battery and connect the alternator and run the car and check it that way.


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    Re: dimming lights

    Post  scy135 on Tue Feb 02, 2016 8:53 pm

    Yea so my lights dim and radio cuts out when I brake I added an aftermarket voltmeter and it runs at 14v with no lights on and 13 with lights on. When I press the brake pedal my lights drop another volt. So I it a bad alternator?
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    Re: dimming lights

    Post  scy135 on Sun Feb 07, 2016 8:56 pm

    I changed the alternator and its still doing the same thing the volts go way down when you turn the lights on and it drains my battery I took it for a quick spin and my battery was like at 11.6 volts what could be going on?
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    Re: dimming lights

    Post  HeavyChevy77 on Sun Feb 07, 2016 9:55 pm

    U have a short bro
    U say voltage drop when you brake and have lights on
    It could be brake light wiring shorted
    See if any brake lights are out check taillights with headlamp switch on and look for and bulbs out
    Shit if you wanna go balls out and know for sure use and ohmmeter / multimeter on the resistance measurement setting , red one on the positive and black on negative , and there should be OL (out of limits) but 0 or close to it is a short to ground. I didn't really mater if you hook it up backwards ,what does matter is that you have the power off/switch off
    If you suspect and shorted power wires , disconnect the battery and connect one test lead to the positive cable being tested and other test lead to a could ground
    Hope this helps
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    Re: dimming lights

    Post  cammrjeff on Mon Feb 08, 2016 11:57 am

    The 1st thing I would do is make sure the Belt isn't slipping under load, could be as simple as a glazed belt. If those are OK
    I would Replace the battery cables if they are over 8 years old or of unknown Vintage. High resistance in battery cables can cause all kinds of odd problems, also check the chassis and engine ground straps, bad grounds can also cause all kinds of odd issues.

    I just solved a battery draw down issue on my 78 Pontiac by replacing the original battery cables, the car only has 39,000 miles on it but the cables were 35+ years old. I was actually looking to solve a Hot Starting issue that turned out to be something different, but the car always had a draw that would kill the battery if I didn't start it for 3 days.

    My Hot start issue was caused by a Cracked passenger side exhaust manifold that was blowing hot air on the starter solenoid. I replaced the manifold, and Solenoid, along with the Battery cables, and installed a heat shield on the Solenoid. I also found one of the engine ground straps broken and replaced it. Now the starter works perfectly, and the battery drain is gone.


    Last edited by cammrjeff on Mon Feb 08, 2016 12:05 pm; edited 2 times in total (Reason for editing : No belt tensioner on a 78 sorry)


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    Re: dimming lights

    Post  Xtreme Thunder on Mon Feb 08, 2016 12:31 pm

    Does the '78 have an external (separate) voltage regulator or is it part of the alternator?


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    Re: dimming lights

    Post  cammrjeff on Mon Feb 08, 2016 2:37 pm

    No external Voltage regulators after 1968 on GM products that I am aware of, my 78 uses an internal regulator.


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    Re: dimming lights

    Post  scy135 on Mon Feb 08, 2016 3:57 pm

    I believe the regular is built in to the alternator. And yes the belts are old I was thinking it could be the belt because at idle the alternator charges at 14 volts once I hit the gas the belts squeak and volts drop so I looked at belts and they look ancient. Same with the battery cables. I'm really new to electrical work so I'm not too good at finding shorts yet. I'm hoping it wont be a major issue
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    Re: dimming lights

    Post  scy135 on Mon Feb 08, 2016 4:00 pm

    Oh but at idle of I row the windows down volts drop as well. But then again it seems like they bind maybe the window motor is being overworked

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