2000 Silverado C1500 Electrical issues

Discussion in 'General Chevy & GM Tech Questions' started by 99vortec, Jan 2, 2010.

  1. 99vortec

    99vortec New Member

    Hi, working on a C1500 with 4.3. Had a dead battery this morning so I cleaned up the bat terminals and jumpstarted it and the Message Center battery light was lit and the guages/lights were jumping/flickering all over the place. Had Autozone test the alternator and it was fine on their bench tester so I put a new battery in it, reinstalled the alternator and had autozone test with the handheld unit in the vehicle while running. They said the alt was putting out a little low. Looked to be in the low 12s.

    Bat light on the dash stays on most of the, only going out very briefly every once in a while, and voltage gauge and dash lights were still jumping around.

    So I swapped out the alternator. No joy, same symptoms. If I kick the rpms up to 1k the volt gauge shows around 14 which is what I would expect so I think it's charging okay and functional but the visible symptoms are troublesome.

    I'm suspecting a bad ground somewhere.

    Thought some of the more experienced folks on the board might have some good pointers or connections to inspect etc.

    I hate, hate, hate, electrical gremlins! :)
    Last edited: Jan 2, 2010
  2. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Is the new battery fully charged?
    I know sometimes a partially charged new battery will cause issues, but once it's fully charged those problems should go away.
  3. 99vortec

    99vortec New Member

    Good question. I was going to leave it on the charger overnight to make sure but it turned over pretty strong.
  4. 99vortec

    99vortec New Member

    Well, I left a charger on it all night and the gauge doesn't seem to be fluctuating *as much*. A voltmeter across the battery at idle showed it jumping around by about a 10th of a volt. BUT the battery idiot light on the message center is still on/off and mostly on.

    It's got about 88k miles on the original belt (near as I can tell, it's my Mother-in-Laws truck, just to add insult to injury). Could the belt be stretched out, causing the fluctuations and the idiot light be so sensitive that it's triggering a false positive on the minor fluctuations?
  5. 99vortec

    99vortec New Member

    More info: I just pulled the radio fuse, took the key out of the ignition, shut the doors, disconnected the under-hood light (cause I don't know if it's switched or not) then disconnected the negative battery cable and measured the voltage across it. It showed an 11.5 volt drain with nothing on. My experience with modern cars is pretty limited, but on a '79 IH Scout that means a dead short somewhere. Does anythinig else draw that much? Computer?
    Last edited: Jan 3, 2010
  6. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Yes thats a short somewhere
    Whats the AMP drain?
    Start pulling fuses and reading the battery with each fuse you pull.
  7. 99vortec

    99vortec New Member

    So just for kicks I disconnected the field/exciter wire off the alterator (cause I had a mishap on my old scout once and got the 2wire connector on backwards and it took MONTHS of leaving the battery charger on at night before I found that!) and the drain went away. However, with the field wire unplugged, I've got no continuity to ground from the plug. Doesn't make sense...
    Last edited: Jan 3, 2010
  8. 99vortec

    99vortec New Member

    False info. Just ran the same test again unplugging the field wire and the drain stayed. Pulled each fuse and the drain stayed.

    I hate electrical gremlins. All the electrical stuff is working fine, but my wife just told me that the battery light has been going on and off for months. Nice of her to let me know. :)

    I crawled underneath and didn't see anything amiss, other than what appears to be a leaky water pump and leaky rear main seal.

    Oh, and my OBD scanner shows no pending codes.
    Last edited: Jan 3, 2010
  9. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Yours is about the third or fourth post in the last few weeks with similiar issues.
    Do you have a factory alarm or anti theft system?
  10. 99vortec

    99vortec New Member

    Pretty lacking in frills. Doesn't even have power windows.

    I put a belt on it today since the original GM belt had 80k on it, and took it out to go bird hunting and put some miles on it. When I drove out about 20 miles the idiot light was flickering quite a bit. Parked for a while, then on the way back it didn't come on once till I got almost to town, then it went crazy. The headlights would dim, the idiot light would come on, then the headlights would brighten and the idiot light would go out, in that order.

    Leaning toward the "if you can't figure out what's wrong, fix what you know isn't right" scenario, I'm starting to wonder if the water pump leaking out the weep hole isn't getting something wet intermittently. Crank position sensor maybe?

    My mother in law said, today, that it's had a "slow leak" in the coolant and that the battery light has always come on and gone off ever since she bought it a while back.

    Just googling around I did see several posts on various forums with the exact same symptoms but no resolutions.
    Last edited: Jan 3, 2010

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