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Thread: 86 glhs power loss light.

  1. #1
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    86 glhs power loss light.

    Got glhs 116 runnin after 20 years of sitting. It runs pretty decent at that. The issue I'm having is while sitting at idle the power loss light flickers. If the radiator fan kicks on it stays constant till the fan cycles off. With the lights on or the hvac blower on it will also stay on constantly. With lights and the hvac blower on high the voltage drops to 12.5 or so. The voltage hangs out there and will not recover. The voltage at the field terminals under load is 10 volts. At Wot it will also throw the power loss light then go away once you let off. Had the alternator tested at an auto parts store and they say it's good for what it's worth. The battery is new. No codes currently. I don't have much information on the car as the po died. I'm thinking the stock alternator just isn't cutting the mustard anymore but would like to know if I should check anything else. Rather not throw parts at it. Thanks brandon
    Last edited by bgbmxer; 11-15-2020 at 08:12 PM.

  2. #2
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: 86 glhs power loss light.

    No codes?

  3. #3
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    Re: 86 glhs power loss light.

    No codes forgot to add that in there.

    - - - Updated - - -

    Quote Originally Posted by cordes View Post
    No codes?
    No codes

  4. #4
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: 86 glhs power loss light.

    If it's the stock alt, I wouldn't be surprised if it couldn't keep up. They were marginal when new, sucked 20 years ago and probably have a hard time keeping up due to the demands of an old system. I would replace it with a Nippondenso unit and go through some of the connections you can easily get to while you're at it. The old electrical in these cars is really starting to show its age.

  5. #5
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    Re: 86 glhs power loss light.

    Your not the first person to say this. I just didn't wanna throw parts at it all to not fix a problem. I do want to upgrade tho. It's a low mileage car but age is age

    - - - Updated - - -

    Quote Originally Posted by cordes View Post
    If it's the stock alt, I wouldn't be surprised if it couldn't keep up. They were marginal when new, sucked 20 years ago and probably have a hard time keeping up due to the demands of an old system. I would replace it with a Nippondenso unit and go through some of the connections you can easily get to while you're at it. The old electrical in these cars is really starting to show its age.
    Your not the first person to say this. I just didn't wanna throw parts at it all to not fix a problem. I do want to upgrade tho. It's a low mileage car but age is age

  6. #6
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    Re: 86 glhs power loss light.

    Brandon,
    You had alternator tested off car or on car? Power module controls the regulator function. Should be around 14.0 volts output. A reasonably light load like blower motor or fan motor should not be making alternator run at 12.5 volts. Start looking at alternator sub harness wiring, grounds, power module since you already had alternator tested. All that grease they put on connectors more resembles wax after 35 years. Esp check connections at alternator and black 8 way connector by battery.
    I agree though, the Chrysler l-body alternator sucked 35 years ago. I was lucky to find some NOS Mopar alternators at a shop near my home. The owner had a stash of them as they were a very popular alternator back in the day. Then the market dried up for these when the vast majority of these cars were scrapped. He sold me a couple of them for like $30 each. Had to blow about 1/8" of dust off of the box (lol). Careful when looking for ND alternators. Be skeptical of any "NEW" ND alternators. They look like ND alternators, but almost all these days are just Chinese knockoffs. That rear plate must have embossed ND logo to be the real deal.
    Todd

  7. #7
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    Re: 86 glhs power loss light.

    I took the alternator off and took it to a parts store and registekt checked out ok. I never get to 14 volts with no load and it drops substantially with load and never recovers. I am gonna have to start at the alternator and work my way up.

  8. #8
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    Re: 86 glhs power loss light.

    Quote Originally Posted by bgbmxer View Post
    I took the alternator off and took it to a parts store and registekt checked out ok. I never get to 14 volts with no load and it drops substantially with load and never recovers. I am gonna have to start at the alternator and work my way up.
    Brandon,
    Yes it does sound like rectifiers are bad in alternator. Sounds like a good game plan.
    Good luck,
    Todd

  9. #9
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    Re: 86 glhs power loss light.

    Quote Originally Posted by 4 l-bodies View Post
    Brandon,
    Careful when looking for ND alternators. Be skeptical of any "NEW" ND alternators. They look like ND alternators, but almost all these days are just Chinese knockoffs. That rear plate must have embossed ND logo to be the real deal.
    Todd
    As a note, I thought it would be a good idea to get a reman ND from Denso ( via RA). Worked out well but took a week or so for them to ship.

    Added note:
    You can purchase diode packs for the ND on ebay and repair yourself. The ND is easy to take apart and repair especially brushes and diodes. Good luck
    Last edited by chromguy; 11-16-2020 at 03:56 PM.
    Regards,
    Miles

    DD '87 Sundance T1, 12PSI, SLH with rear disks
    '87 CSX #432

  10. #10
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    Re: 86 glhs power loss light.

    Update. Nothing to update yet. Ordered a new alternator to do the upgrade awhile and have a newer style harness that should work with the nipedenso alternator. Ill report more when i start troubleshooting this weekend or after i install the new alternator.

  11. #11
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    Re: 86 glhs power loss light.

    Quote Originally Posted by 4 l-bodies View Post
    Brandon,
    You had alternator tested off car or on car? Power module controls the regulator function. Should be around 14.0 volts output. A reasonably light load like blower motor or fan motor should not be making alternator run at 12.5 volts. Start looking at alternator sub harness wiring, grounds, power module since you already had alternator tested. All that grease they put on connectors more resembles wax after 35 years. Esp check connections at alternator and black 8 way connector by battery.
    I agree though, the Chrysler l-body alternator sucked 35 years ago. I was lucky to find some NOS Mopar alternators at a shop near my home. The owner had a stash of them as they were a very popular alternator back in the day. Then the market dried up for these when the vast majority of these cars were scrapped. He sold me a couple of them for like $30 each. Had to blow about 1/8" of dust off of the box (lol). Careful when looking for ND alternators. Be skeptical of any "NEW" ND alternators. They look like ND alternators, but almost all these days are just Chinese knockoffs. That rear plate must have embossed ND logo to be the real deal.
    Todd
    Seems as tho my new alternator is a Chinese knock off. Still gonna try it.

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