Alternators burning up on my 1985 Silverado

Discussion in 'GM Electrical Tech' started by Royce Lancaster, May 29, 2012.

  1. So Ive restored my 85 chevy back to mostly factory appearing, plus all my customizations. Ever since I have put the truck back together I have had alternator problems, if they're charging they're squeaking, no matter how tight/lose the belt is. If they're not squeaking, they're not charging. Ive even tried a "one wire" alternator and it burned it up. The other day me and a another guy completely went thru all the wiring and found a few problems and straightened a few things up. I got a new alternator to charge and not squeak and then i tied all my wires up and fired it back up and it squeaked, here is what i have found: if i test the regulator(brown/White/keyed power) wire on the alternator while its plugged in to it, it reads 3.15 volts but if you unplug it, it reads 11.57 volts like the rest of the truck. Whats going on here? is something burned up or not right? The alternator screams, is the 3.15 volt wire not allowing the alternator to fully engage hence the squeaking..


    Last edited: May 29, 2012
  2. Any advice from anyone?
  3. Crawdaddy

    Crawdaddy All hail the Mad King!! Staff Member 5+ Years 1000 Posts Platinum Contributor

    Sounds like you may have a wire that has some insulation missing. If it worked while the wiring was loose and down, but not when it's bundled nice would indicate that to me. Just gotta chase down wiring and find the bad wire.
  4. kw70chevy

    kw70chevy Member

    you have a hot wire grounding check down by the starter make sure there is nothing touching.
  5. RallySTX

    RallySTX Member 100 Posts

    Let me get this right, you have a 85 Chevy, with a v belt alternator, and the belt squeals when it's charging, but if you tighten up the belt, the alternator still turns but it doesn't work? What I know is this, V belt alternators squeal when the draw or load on the alternator exceeds the belts grip, so the belt squeals due to slip. Is the belt new or old? Has the battery been checked by a GOOD tester? Have you added aftermarket sound, lighting, or anything else that might place more of a load on the electrical system than a stock truck? If so, you may need to add a second alternator and battery to keep up with the load.
    Turn the truck off completely and remove the battery cables from the battery, and check them with a meter to see if you have a leak. Sounds to me like a short somewhere is causing a huge drain on the charging circuit. Have you replaced the main battery cables? Do you mean to say the truck burned up the one wire alternator, or the one wire alternator burned up the belt? What do you mean by this exactly? "
    I got a new alternator to charge and not squeak and then i tied all my wires up and fired it back up and it squeaked,
  6. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    Exactly, this is your problem, you proved it with the "it reads 11.57 volts like the rest of the truck" statement.
  7. The battery is brand new, just replaced it trying to track this problem down. Cables are fairly new, not worn.

    This was a 78 amp factory style alternator. Yes I have a Sound system but its all on a separate circuit and the alternator still acts the same when it is unplugged.

    Second thing I checked.

    As of RIGHT NOW I have fixed this issue with Replacing the Alternator again, so far so good.
  8. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    Ok, but a fully charged battery should read 12.5x, not 11.57, was this a typo?
  9. Its just what the battery was reading at the time, from constantly starting the motor with out the alternator charging, and driving around for a day with out it charging.
  10. RallySTX

    RallySTX Member 100 Posts

    Yeah, I was afraid of that one, I have had a couple people go through several new alternators before they actually got a good one, that happens. I hope the trouble is fixed.
    Brian L.

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