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77 K5 electrical woes

Discussion in 'The Garage' started by jonny290, Apr 16, 2007.

  1. jonny290

    jonny290 Registered Member

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    Location:
    fayetteville, ar
    Vehicle: 1977 K5 Blazer, auto, NP205 case installed, A/C. Sub-10-year-old 350 installed, runs fine, if a bit gas-guzzling.

    The problem: Roughly two months ago in the middle of the Midwest cold snap, my Blazer bit it one night. We took the battery to Autozone, they tested, said "recharge and test" but that it was probably alternator. Reman alternator goes in, get a jump, truck runs fine for a month.

    Couple of weeks ago, I notice the battery voltage being a little low, even when running. Like, 10.5 to 11 volts with no headlights, 9-10 with headlights. I figure "Battery may just need a good charge" and overnight trickle it. No help. Battery full-on dies 48 hours later, Autozone says a cell is gone. New battery goes in.

    Last week, I got into the truck and battery was dead. Jumped it, voltage was extremely low. I had to 45-mph it home with dim headlights - put it this way, my voltage was so low that periodically my stereo head's "I'm turned off" circuit would trip and the security alarm would beep. It stayed running the whole time and I couldn't have charged up the battery enough with the jump to get it all the way home, so I'm guessing that the alternator kept it alive on the way home, and that I'm not getting the battery charged.

    It's in the driveway now, battery disconnected. I was just wondering if somebody could lay out the very basic components of a 70's Chevy starting/charging system, so that I can isolate what's going on. I get a small spark when connecting the B+ line to the battery with no key in, and I'm wondering if that's the stereo's memory circuit or maybe a short. It doesn't seem like the stereo memory would pull more than a few hundred mA at most. I suppose that I can unhook the stereo and test - just realized that while writing this.

    Thoughts? Is there a regulator or something that might be blown out or partially failing that I'm missing? I'm not really averse to rewiring the truck if need be - this is about the only issue it has and I have a backup vehicle - but I don't want to start slicing up wiring harnesses without a solid game plan. Just give me some suspect part names to look at (e.g. do they call it a charging regulator? voltage regulator) and I can start diggin'.
     
  2. jonny290

    jonny290 Registered Member

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    bump, thoughts? going home for the night.
     
  3. AZ79K5Project

    AZ79K5Project 1/2 ton status

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  4. Chevy305

    Chevy305 6 Lug 14bsf Status Premium Member GMOTM Winner

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    I've heard that those Auto Zone reman alternators are crap and don't last long if they work at all...
     
  5. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    Its 30 years old . Its been exposed to oil , water , heat and cold .

    Either your going to replace the whole harness at one time , or like most of us , just start repairing the crap sections as you can .

    I would start by removing the battery cables , the wiring to starter , alternator , and junction block . Clean , repair or replace . It could be cheap to free depending on your garage , friends garage , parents garage , or your junkbox .

    A man is only as good as his junkbox :thumb:
     
  6. jonny290

    jonny290 Registered Member

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    Thanks for the links and tidbits. That should get me started.

    Since it appears that my '77 has an internally regulated alternator, I'm going to take it to autozone and have them test it. Then if it tests good I'll start replacing wires.
     
  7. AZ79K5Project

    AZ79K5Project 1/2 ton status

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    Post up what you find.
     

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