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SI to CS Alternator Swap

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by TrcksR4ME, Jun 22, 2003.

  1. TrcksR4ME

    TrcksR4ME 1/2 ton status

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    I tried this post in the Garage but got no response, so I'll try here too /forums/images/graemlins/smile.gif

    I am going to swap on a CS series alternator and am wondering how big of deal this swap is. I did a little research and found that I will need to get a conversion plug for my SI style wiring.

    Also in this research there was something about gettin a conversion plug with or without resistence built into it in order to energize the alternator and make it work right. It needs a minimum of 35 ohms from what I read. The article I found said that if you have a battery light in the dash, this serves to create resistence and you are ok. I do not know if my '77 Blazer has this, and I do know that if it does it is broken. How would one check the wiring to see if there is resistence in it? Any other comments on this swap in general? Thanks!
     
  2. imiceman44

    imiceman44 1 ton status

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    I believe 77 didn't have the light, only amp meter, and that doesn't create enough resistance.
    I would say get the one with resistor.
    I have seen that site before and they have all you need for the conversion, but I didn't do it because I can rewire for checper using junk yard parts, but for a bolt on system they are good.
    /forums/images/graemlins/thumb.gif
     
  3. prjt_blzr

    prjt_blzr 1/2 ton status

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    Your 77 most likely uses a volt meter. GM kept the altenator from back feeding the electrical system by installing a resistive wire from the ignition switch to the volt meter and to the main harness block. If you use your original altenator wire the system may or may not work correctly. It all depends on what voltage the altenator lights off at. The safest bet is to use a different keyed wire and use a diode in series to prevent back feeding the electrical system. Most CS altenators need more current than the older SI types and that is what makes your original wire a crap shoot. Or you can do what I did, I tapped another wire into the ignition block and dedicated it for the new CS altenator and place a diode in series so that the altenator could not back feed the system. If you do not get this correct, the only way to shut the system down is to disconnect the altenator or coil wire.

    If you have an idiot light then you are all set and only need the single wire adapter.

    Good luck,
    Mike
     
  4. TrcksR4ME

    TrcksR4ME 1/2 ton status

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    If there is a battery light it is burned out or doesn't work. Do you think the adapter with the resistor built in would do it then? I am not very technical when it comes to wiring /forums/images/graemlins/crazy.gif On the adapter the resistor is inline with whatever wire the old alt used, thats all I know LOL
     
  5. prjt_blzr

    prjt_blzr 1/2 ton status

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    The adapter with the resistor will work if you use a switched wire that goes straight to 12V and not the original wire (assuming you have gauges). Do you have gauges or lights in the dash? If you have lights, (not too common) then you can just wire up the one wire with no resistor. If you have gauges then you need the resistor adapter.
    Mike
     
  6. TrcksR4ME

    TrcksR4ME 1/2 ton status

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    Have gauges, only idiot light I've ever seen work was the brake light. When I turn the truck to the on position one light comes on and its not a battery light, either brake or seat belts or something.

    And as far as alternator wiring goes I have no idea what the wires coming off the alternator are for. There is the charge wire that goes to the firewall and then to the battery, but the 2 wires on the plug?? One is larger than the other but I have never looked to see where they go /forums/images/graemlins/crazy.gif

    I guess I am not very wiring smart LOL /forums/images/graemlins/grin.gif but a few years ago I didn't know anything about trucks at all so I appreciate the help /forums/images/graemlins/thumb.gif
     
  7. BobK

    BobK 1/2 ton status

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    One goes to the eng. light in the dash the other is the "sense" wire.
    The "sense" wire takes voltage from the main power output and routes it to the internal voltage reg.
    Then the voltage reg. will either allow more voltage or less voltage to be produced by the alt.It all depends on the demand on the alt(like what's on,heater,lights,stereo amps,etc.)

    White wire I believe is the one that goes to the dash light.
    The blue wire is "sense" wire
    These wire here right?
    [​IMG]
     
  8. prjt_blzr

    prjt_blzr 1/2 ton status

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    O.K. There should be three wires going to your factory SI alt. The single big red wire is the alt output. This eventually finds its way to the battery to charge it. There is also a small two pin connector that plugs into the side of the alt. There should be a thin wire and a heavier brown wire in this plug. The brown wire finds its way back to the wiring harness block on the firewall and then to the ign switch. This wire excites the alt when you first start the engine. After the engine is started, this wire no longer needs to supply 12V to the alt. Gm used a resisitive wire to prevent the alt from pushing current to the vehicle after the engine was started. This allows you to turn the engine off /forums/images/graemlins/shocked.gif

    The CS alt will need the adapter plug to allow an easy hook up. If you upgrade the current rating on the alt you should run a larger wire to the battery to prevent the factory red wire from melting. The adapter plug will have two wires coming off of it. One wire (varies by MFG of the adapter plug, mine is yellow) goes to the same post as the big red wire. This provides the 12V sense lead for the regulator. The second wire will go to a switched 12v source on the truck (again, color of this wire will vary but mine is brown). You can try to wire this into the factory SI brown wire and see if it works. The risk is that the alt may not charge if the battery is low. The best way to do this is to probe around on the fuse block and find a power tap that is hot when the engine is running and then run a new wire to the alt plug.

    If I didn't forget anything the system should now run with no problems /forums/images/graemlins/cool.gif
    Mike
     
  9. DUKSRULE

    DUKSRULE 1/2 ton status

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    Where do you get the adapter plugs? I am trying to put an 89 alternator with serpantene setup in my 86 pickup and the plugs don't match. If I could get an adapter or someone tell me how to wire it that would be great.
    Thanks
     
  10. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    [ QUOTE ]
    I am trying to put an 89 alternator with serpantene setup in my 86 pickup and the plugs don't match.

    [/ QUOTE ]

    What's the plug for the '89 setup like? I had to get a conversion plug to hook up my '87 to the '94 Pontiac Transport alt. that I have.

    You can order it through gmpartsdirect.com or your local dealer. The part number is 12083462. It cost me 20 bones. Might want to try that.
     
  11. DUKSRULE

    DUKSRULE 1/2 ton status

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    Does it just plug into the old plug or do you have to run wires? If so are there directions?
     
  12. prjt_blzr

    prjt_blzr 1/2 ton status

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    I got mine from a local shop in Colorado Springs when they built my 200A CS144 alt. This guy just reached into a bag of tricks and handed me a preassembled plug and wires to hook up the CS alt. in place of my old SI. I would imagine that any good rebuild shop should have them though.
     

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