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Help needed with electrical problem

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by djohnsn, Oct 4, 2000.

  1. djohnsn

    djohnsn 1/2 ton status

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    I have an electrical problem that I have not been able to solve. My headlights slowly dim until they are completely off - the truck then dies. After recharging the battery, I can drive again with headlights for 15-20 minutes before the truck dies again. I replaced the alternator, but this did not solve the problem. I had the battery checked by two different auto parts stores - both said that it was ok. I can't find any obvious problems with any wiring. This is on my 71 pickup (daily driver). I don't know if the problem only occurs when using the headlights since both my drive to work and home was in the dark.

    Has anyone else solved a problem similar to this? Ideas?
     
  2. Michael

    Michael 1/2 ton status

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    It seems like it's gotta be a charging problem. I would make sure the big charging wire (red) from the alternator is good. I think it should go from the alternator to the starter, where the big positive wire from the battery connects. You should be applying around 14 volts to the battery while the truck is running. My book shows an external voltage regulator on a '71, if that's true with yours it could be the culprit. Also, make sure you have a good ground from the engine/alternator to the battery. Repost or email me if none of the above works out.

    Michael [​IMG] http://jmartin.net/parker/goose.htm
     
  3. scavenger

    scavenger 1/2 ton status

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    I think the post from Michael may have explained your problem. I was having the same problem you are experiencing on my 69 C50 dump truck. I then went to an alternator repair shop and purchased a conversion kit that allows you to eliminate the external voltage regulator, and replace the older alternator with a newer one with the internal voltage regulator. all that was involved was swapping in the new alternator, connecting the adapter to the alternator that converts it to the newer style connector, then disconnecting the harness that plugs into the external voltage regulator, remove and discard old external regulator, then plug in adapter to the harness you removed from the old voltage regulator. It is a real easy conversion and takes approx 30 minutes unless you have to remove the pully from the old alternator and put it on the new one. The newer internal type alternators are more available and dependable according to the guy at the alternator shop. The conversion kit cost me $26.00 from him, but I later found it somewhere on the net for $14.00. I also found out that if you also plan on converting from the old point type distributor to an HEI distributor, you have to convert to the internal voltage regulator anyways because the external voltage regulator type alternator will burn out the module in the HEI distributor. Hope this helps.
     
  4. Blazer1970

    Blazer1970 1/2 ton status

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    Or if you want to avoid all that screwing around, just replace your voltage regulator. The parts store should have the original mechanical type, or an electronic version that is a direct replacement. The regulator is on the radiator support near you drivers side headlight. There is no problem running an original style regulator with an HEI.

    Tim

    1970 Blazer CST 4X4 350 SM465 NP205
    1987 Suburban 4X4 350
    1988 Chevy Pickup 4X4 350
     
  5. djohnsn

    djohnsn 1/2 ton status

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    I still have not solved the problem. I took my new alternator back to have it tested and it was bad (AC Delco reman.) I put on a cheap Autozone alternator while I had the AC Delco alternator off, but still experience the same problems. Voltage regulator is almost new, but I don't know an easy way to verify that it is good. Could a bad voltage regulator be killing my alternators?

    I would prefer not to covert to an internally regulated alternator on this truck at this time.
     
  6. Blue85

    Blue85 Troll Premium Member

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    Yes.

    '85 JIMMY
    '90 paint/grill/trim 5"susp 33/12.5/16.5
    Fresh 350 B&M '87 TH700
     
  7. sosamantx

    sosamantx 1/2 ton status

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    <font color=blue>Don't know if you have fixed your problem yet, but Autozone should be able to check the voltage regulator for you.You will have to take it off though. - Steve</font color=blue>

    <font color=blue>Steve Sosa a.k.a. "sosaman"</font color=blue>
    http://sosaman.home.texas.net/carpics.html
     

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