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Electrical Problem?

Discussion in 'The Garage' started by k5baby, Dec 3, 2005.

  1. k5baby

    k5baby Registered Member

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    Location:
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    My 72 k5 blazer is not reading 14 volts when cranked. I replaced the alternator, new battery, new wiring harness and I can't still get it to charge. Eventually after driving it with the headlights on the battery will die and I have to recharge with battery charger. When you take the positive off the battery it will also die. It has to be a wire where do I start? I've checked the grounds. The guy at the parts house wanted to no why I had a voltage regulator on the core support and one built in the alternator, a total of two. I'm kinda curious myself. Thanks in advance for any suggestions.
     
  2. diesel4me

    diesel4me 1 ton status Premium Member

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    old truck--later alternator!..

    Up until 1972,GM used "external" regulators..after that,the used regulators that were built in the case of the alternator..its easy to swap the newer one into an old truck.(both bolt right in the same way)...some folks "cheat" and use the old wires at the regulator to wire up the 2 prong plug on the later style altenator...they might have done it wrong,or maybe your old wires are gangrene,shorted,or broken-here's what to do..

    Turn the key on..you should have 12 volts at BOTH wires on the 2 prong plug on the alernator--use a test light,or multimeter to see..I bet the smaller brown or white wire is "dead",and has a short or break in it somewhere..no cuurent there = no charging!...

    If the thick red wire at the plug is dead,look for burnt fusible links at the solenoid,and near the brake booster,there should be one at the plastic junction block there,and inspect the wire itself....the thick red wire that bolts to the stud on the rear of the alternator should have 12V constantly,even with the key off..if that wire is dead,its either cut,shorted,or the fuse links are toast..

    With the engine running,put the test light from the battery positive to the brown or white wire on the plug,if it had no juice during the earlier test..I bet the alernator kicks in and starts charging,because you just gave it the 12V it needed to energize the feild coils to make it charge..

    It sounds like someone "upgraded" your truck to the newer style alternator,but wired it in with the old harness,and now it has 2 regulators ,or its not getting power to the wires I just described correctly..I re-read your post after writing a whole page on how to wire up the later alternator in your truck--then I saw "new wiring harness" :doah: ...if you still have trouble ,just ask,I'll try to help.. :crazy:
     
  3. k5baby

    k5baby Registered Member

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    Location:
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    When key is on not running I need to have red voltmeter wire on one of the two prongs and black voltmeter wire on a ground? Then do the same on the other prong? And I should get 12v at each one?
    The wire harness that is new, plugs into the firewall goes to the voltage meter on the core support then the same wires( at least same colors, the rest is wrapped up in tape) goes to the alternator (blue/white- plug, red -bolts onto back of alternator, black- ground). Is that the way it's supposed to be?
     

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