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  1. #1
    Jr. Apprentice hihoslva's Avatar
    Join Date
    Jul 2008
    The surface of Mercury - AKA, Arizona.

    Default Do I have an electrical problem or normal?

    Hello all. I'll keep the long story as short as possible.

    1999 Suburban C1500, 163,000 miles.

    Recently, I noticed some voltage drop (by the dash gauge) when using certain accessories (like the blower) at idle. Revving the engine helped, as did shutting off the accessories. At night my lights would dim with the blower on, etc. Figuring my alternator was about to take a crap, I just replaced it. The truck had a the 105 amp alt, but since the swap was bolt-in, I installed the 140 amp CS144 alternator.

    The wiring harness (single wire but 4-prong harness - go figure) is not the same. My buddy has a '99 with factory 140 amp alt I could use for reference, so I cut my factory harness off, crimped on a connector, insulated it, and plugged the wire on to the same terminal of the alt as his (the middle prong of the three "small" prongs).

    Truck is running good, and my voltage is 13.75 tested with a multi-meter at the battery terminals. This is with or without accessories running. Is this the correct range?

    My main concern though is HEAT. The alternator is HOT HOT HOT. I mean burn-your-hand hot after idling for only a few minutes. My 4-gauge fused cable running from the battery to the alt is also quite hot. Not melting, but hotter than I expected.....

    Is this normal? I don't remember my 105 amp alt getting that hot, but I never really checked it....

    Should my alt be scalding hot at idle? Do I possibly have another issue I should investigate? Is the voltage of 13.75 correct (dash gauge reads between 12 and 13, but the multimeter reads 13.75)?


  2. #2


    Is it 4 gauge copper wire?

    Aluminum wire would need to be a larger gauge.

    According to the following wire size chart, 4 gauge should be plenty...

    And is it hot just near the connections? Or the same hot the entire length of the wire?

    Poor electrical connections will create heat and this will travel. Probably the reason for the 4 connectors!

    And as you get into higher amperages like 100 amps, a "tight" electrical connection is not good enough. You actually need to torque connections to a specific tightness!

    I have seen high amperage DC connections (in the large computer world) which were "regular guy" tight, but this was not good enough. The connection was hot to the touch. Tightening the connection to the manufacturer's specified tightness with a torque wrench made for a better cool connection!

    But don't go tightening things without the correct specifications. Because some people (king kong men) will tend to tighten things too tight and strip the bolts.

    If there is a bad connection like at the crimp connection (see if this area heats up first), you would be able to measure a voltage across that connection.

    Here is information about voltage drop testing...

    I would suggest getting the factory wire for this without a crimp connection.

    And/or a larger copper wire.

    And/or a "clamp and torque the heck out it" large wire splice.

    Maybe a couple of the following from the electric department of a hardware store until you can find something better. Overlap the wires and tighten the heck out of them. Then wrap real good with electrical tape. But this is the general idea. A real good tight wire splice...

    92 GMC Sierra 2500

  3. #3
    Jr. Apprentice hihoslva's Avatar
    Join Date
    Jul 2008
    The surface of Mercury - AKA, Arizona.


    Thanks for the advice. I do think my connections are tight. I'm using 4 gauge car audio power cable for the battery-to-alt connection. Yes, I do have a large ring terminal crimped to the alternator side, and it's quite secure. I do have the connection fused as well - 120 amps, close to the battery - since the skinny factory wire included a fusible link.

    The heat is along the entire length of the wire, but my real concern lies with the alternator itself. It's hot. I mean really hot. An hour after I shut the vehicle down, it was still quite hot to the touch. I couldn't put my hand on it for more than 6 or 7 seconds.

    Granted, I live in in Arizona, and my garage was probably 110 degrees, but still - should the alt get this hot?

    I am going to buy the proper pigtail harness for the alternator today and spice it into the single factory wire. However I'm not sure this will make any difference - I'm just going to do it for peace of mind.

    Still wondering about all this heat......

  4. #4


    I don't know a thing about alternators/generators (this is a career in itself!), but I do know with electric motors, if you don't have a large enough power cord, the motor can burn up.

    For example people will use a small gauge extension cord for an air compressor and the electric motor will burn up. And the electric motor is "happier" with a large gauge wire.

    In your case, this would include a larger ground wire to the engine block possibly. See if that is hot too.

    So I am guessing a similar problem may exist with your alternator? I don't know.

    But this would certainly be a good thing to learn about as they are adding more and more electrical gadgets to automobiles. If I get time, I'll poke around on the internet and see what I can learn about this.

  5. #5


    I found some information which says your battery could be causing this. And that you would need to check with an amp meter...

    Hot Alternator...

    About batteries with "shorted cells"...

    Testing batteries for shorted cells...

    Perhaps if you have a second vehicle, you could swap batteries and see if that solves the problem?

  6. #6
    Jr. Apprentice hihoslva's Avatar
    Join Date
    Jul 2008
    The surface of Mercury - AKA, Arizona.


    Thanks for the efforts, Bill.

    Through deductive reasoning, I think my battery was, indeed, shot.

    I did not test it. I just replaced it. Batteries take a beating here in the AZ heat, and mine was 3 years old. I figured if it ain't bad now, it will be at some point, so why not be pro-active.

    After replacing the battery (the old one had some slight but noticeable bulging on the sides of the case), and installing the proper alternator pigtail, I'm running at perfect voltage and not nearly as hot. I'm relatively certain that I had a damaged battery and a failing alternator, and now both have been replaced.

    All seems well in 12-volt land.....

    Thanks for the advice.

  7. #7


    Yes, sometimes you have an electrical problem which causes something else to fail. Then you replace the something else and it fails again! (2 problems!)

  8. #8


    My experience, at least in the past, was that once I replaces a failed alternator, battery and starter were soon to follow.
    When you hear hoofbeats, look for horses not zebras.

  9. #9
    Legend 2ToNe04's Avatar
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    Apr 2009
    Fresno California
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    bigger alt?

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  10. #10


    Quote Originally Posted by 2ToNe04 View Post
    bigger alt?
    If you read the thread, you will see that he fixed the problem. His battery was defective.

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