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Thread: HELP! Cant find electrical problem.

  1. #1
    Registered User glassguy's Avatar
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    Default HELP! Cant find electrical problem.

    71 240Z. My running lights stopped working the other day. I checked the fuse and it was ok. When I pulled one of the bulbs out I noticed it was burned out. It turns out every single running light, and all of the dash lights are not only burned out, but on some the glass is even cracked. I replaced all four of the running lights and they worked fine again, until I started the car and gave it some gas. They got bright and poof. No more lights. The first thing I checked was the voltage regulator. It's only 3 months old. With the car idleing it shows 12.6 volts. The volts dont go up at all if i rev it up. It shows 12.4 to 12.6 at the battery while running. I also just lost my stereo. It went up in smoke the same day the lights started acting up. Also, after all of this, the annoying door buzzer now only comes on when the car is running. And just today after really getting a chance to look thing over, the only thing I can find is that the negative wire that goes from the battery to the firewall is slightly melted. AND, during all of this not one single fuse has blown. And I have the upgraded fuse block with blade fuses last year. I disconnected the entire stereo system and no burned wires or blown fuses. I'm lost. Any ideas ?
    And now, I just replaced one of the running lights and it only come on while the engine is running. at idle the bulbs brightness fluctuates. I know if I reved it up it would burn out.
    Last edited by glassguy; 09-12-2014 at 02:19 PM.

  2. #2
    No more body roll! SteveJ's Avatar
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    1. Do you have a fusible link coming off of the starter and going into the main harness?
    2. How long have you owned the car?
    3. Did you or a previous owner make any other changes to the electrical system such as replacing the alternator? (I saw the "new" regulator was installed.)
    4. Why did you change the voltage regulator 3 months ago?
    5. Have you tested your alternator?

    The multiple system failures (lights, stereo, buzzer, etc.) lend belief that the voltage may have been too high. Corrosion in cables, mixed with higher voltage can create hot-spots, as well.

    Having an external regulator with an internally regulated alternator can cause problems with voltage regulation.
    73 240Z
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  3. #3
    Registered User glassguy's Avatar
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    1. No fusible link that I can see.
    2. 6 years. Restoration finished 2 years ago.
    3. I replaced the alternator a few months ago because the one that came with the car did die.
    4. I replaced the voltage regulator only because I replaced the alternator. Both are "cheap" Oreilly's parts.
    5. Tomorrow morning I will be getting the alternator tested.

    What has me confused is, Why do the running lights ONLY work with the car running. I removed the alternator belt and started the car. No running lights. And with the alternator connected the running lights will work, and will blow if i give it gas. Obviously they are getting too much power. But why wont the damn things work with the motor off! I know I burned a wire somewhere, but I just cant find it. I cant stand tearing apart this car. It's painful.

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    I kind of remember reading some recent posts about new external regulators that had problems. Incorrect wiring, I believe. And you didn't confirm that you don't have an internally regulated alternator combined with the external regulator. I seem to recall that you get either no regulation or no charging when you do that.

    The fact that your lights blow if you give it gas can really only be too much voltage. Each light bulb is just a small resistor that can handle 12-14 volts all day long. But will overheat if the voltage gets too high. You need to have the VR checked, not the alternator, or both. Confirm that they're both good and that the alternator is for external regulator usage.

    Or just go ahead and convert to the internal regulator. Since the external VR's appear to be iffy, that would be the safest route.

    No use fixing the lights problem until you get voltage under control.
    1976 280Z, with some minor modifications

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