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HELP-CUCV 24v problem

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by kickinasphalt383, Sep 1, 2002.

  1. kickinasphalt383

    kickinasphalt383 1/2 ton status

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    I had to take one of my alternators out of my 86 M1008 and after I reinstalled it i have 24volts running to everything?!?! what went wrong? everything that is supposed to only have 12v now has 24v running to it.

    What component of the truck reduces the 24v to 12v into the cab? Is that my problem? thanks
     
  2. Txstruck

    Txstruck Registered Member

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    Sounds like when you hooked the batteries back up, you hooked them in series instead of parallel. Ive seen it before. Im an ex Seabee and own a M1028 CUCV. /forums/images/icons/cool.gif
     
  3. kickinasphalt383

    kickinasphalt383 1/2 ton status

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    Thevy are supposed to be in series for 24volts!
     
  4. 95 Silverado

    95 Silverado 1/2 ton status

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    I'm not sure about military vehicles, but on big trucks that use 24 volt starters, the starter is the only component that actually uses 24 volts. the multiple batteries are routed through a series parallel switch that supplies 24 v. to the starter when cranking, but 12 v. to everything else. you probably made a misconnection when hooking the wires back up.
     
  5. DieselDan

    DieselDan 1/2 ton status

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    Yes they are wired in series for 24V. But you are also pulling 12V from just one of the batteries (for the 12V system). There should be a smaller gauge red wire attached to the rear IIRC battery. We swap the batteries around during an Annual service to get more life out of them.
    And for the record: 24V is used for the starter, glowplugs, slave recepticle, and tranciever hookups. /forums/images/icons/wink.gif
     
  6. kickinasphalt383

    kickinasphalt383 1/2 ton status

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    yeah that is what I thought about the small wire off of the battery. but then how in the hell do i have 24v running to the cab? I didn't mess with the battery cables only the alternator.
     
  7. ZZ4x4

    ZZ4x4 1/2 ton status

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    Just a clarification, the glowplugs run off 12v instead of 24v. I've heard both ways, so I checked it out with my voltmeter.

    Kickin, Just a hunch, but is your alternator the same one in the same position as before? I haven't verified, but I was told that CUCVs could have one 24v and one 12V alt. Check the outputs. If they both are putting out 24v then they both must be connected to end of the battery pair. If one is 12v, this one should be connected to the red wire in the middle. May want to unhook the alt and verify you are getting 12V inside the cab with all other wires in place to verfiy the batts are connected properly. After you connect the alt, see if you have 24 volts on a single battery. This would mean the alt is not connected to the right place or is the wrong alt.
    JT
     
  8. René

    René 1/2 ton status

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    Take the electricity for your 12V plant only from one battery (the positive pole, which is the nearest at negative)
     
  9. René

    René 1/2 ton status

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    The glow plugs functioned with 24V, the glow plugs has 10,5V and between them there is a resistor.
     
  10. Dirty Dave

    Dirty Dave 1/2 ton status

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    According to my 24 to 12volt conversion manual availiable from www.roscommonequipmentcenter.com

    The alternators and batteries are connected in a series to create 24 volts. The drivers side alt. charges the front battery. This battery and alt. supply power for all 12v components. The glow plug and glow plug relay are 12v. Their 24v power supply is reduced to 12v by a resistor bank. The resistor is mounted on the firewall directly behind the motor.

    I would recommend converting to 12v. Roscoe common offers a damn good conversion manual that offers 2 types of conversions. It is availiable on their web-site in the on line reports section as News Note 10

    I hope this info helps.

    Dave
     
  11. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    I converted mine by just switching in a Junkyard harness along with my TBI 350 conversion. Seems like the easiest/cheapest way is to find a good j/y harness...
     
  12. kickinasphalt383

    kickinasphalt383 1/2 ton status

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    First of all, thanks for all the info from everyone.


    Now for what i have done. The initial way i connected my alternator i got 24volts in the cab and on the connector on the firewall (before the glow plug relay) and to everything in the cab. only 12v was coming from the small wire off the battery and then 12v from somewhere else???

    The second way i wired the alternators i get 12v to the connector on the firewall, but nothing in the cab (ie nothing when i turn the key).second way i wired alternator (switched red wires for initial way)


    you will also notice that the resistors on the firewall have been bypassed. it has been bypassed since the day i bought the truck (3yrs ago) and has never been a problem. So the glow plug relay gets its 12v from the small red wire off the second battery. Bypassed resistor and firewall connector

    Batteries

    So which way is the correct wiring route? Why do i get 24v the first way and no juice in the cab for the second way? Thanks

    Also i don't know if i should even be posting this problem YET, since my alternator is bad. the bearings went bad (no electrical problems originally) but when the alternator shop took it apart something could have been messed up causing my current problems.
     
  13. DieselDan

    DieselDan 1/2 ton status

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    Each altenator put out 12Volts (one for each battery). If you measure voltage off the back one will measure 12+V the other 24+V.

    And for the record: the glow plugs are wired to the 24V circuit due to the amount of amps they draw (then they reduced to 12V via the ballast resistors).
     

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