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Question about VSS and buffer box....

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by fortcollinsram, Jul 18, 2003.

  1. fortcollinsram

    fortcollinsram 1/2 ton status

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    Well I am going to be hooking up a VSS again after my auto/to manual and SBC to BBC swaps...I think I found the factory location of the signal orgin...I found a connector under the dash that had three wires (Black, Red, Green) and 2 little sensors on the end of the connector (it kinda looks like the laser head in a CD player). These wires go to a pastel Green box (kinda looks like my great grandma kitchen sink /forums/images/graemlins/eek.gif). I assume this is the buffer box, correct Okay...out of the buffer box there are 4 wires on two separate connectors... One connector has three wires (brown, red s/blk, blk s/white) and the other connector has a yellow wire on it...I know the brown in the reference for the ECM, blk is probably ground, red probably 12V+.But what is the yellow wire for?

    I will get some pics up soon...

    Chris
     
  2. fortcollinsram

    fortcollinsram 1/2 ton status

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    HERE is a pic of the buffer box... The 2 connectors then plug into the end (the left side) of the green box...But what is the yellow wire (NOT PICTURED) for?
     
  3. u2slow

    u2slow 1/2 ton status

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    Your speedo is driven mechanically, right?

    I'm wondering if you need that thing at all. I know it figures into the cruise control, TC lockup, and ABS... possibly even EGR timing, but I'm not sure. /forums/images/graemlins/thinking.gif

    Since it looks like you're going with a BBC and manual trans.... I just can't imagine what purpose it serves.

    BTW: Not all trucks had the buffer.
     
  4. fortcollinsram

    fortcollinsram 1/2 ton status

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    I know I don't need the buffer...I just want to know what all the wires coming out if the buffer are, esp. the yellow one (again, not pictured) The brown is the one that I am going ot hook the VSS adapter to at the t-case and the speedo cable runs thru that....The buffer just converst the mech. motion of the speedo cable to a elec. signal for the ECM...but I need to know what the yellow, brown, black and red wires are for coming out of the buffer...

    Chris
     
  5. u2slow

    u2slow 1/2 ton status

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    [ QUOTE ]
    The buffer just converst the mech. motion of the speedo cable to a elec. signal for the ECM

    [/ QUOTE ]

    87-90 base-model R/V trucks (especially 1-tons) with a TH400 or SM465 did not have a VSS or buffer. Plain cable drive speedo and thats all. ECM operates with no speed input whatsoever. Granted this is a heavy-duty emissions vehicle... although it sounds like your truck is fairly heavy duty as well. /forums/images/graemlins/wink.gif

    My yellow wire hooks into a mystery black-box (a little fatter than a cigarrette pack) above the accel. pedal as part of about a 12-pin connector. I also have a pink wire with a black stripe that ties into the fuse block and the cruise wire on the steering column. The black wire.... that will take some more research.
     
  6. b454rat

    b454rat 1/2 ton status Premium Member

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    I have an 89 K3500, and it has the VSS. I wish it didn't, cause now I have to buy the VSS adaptor so my speedo and truck will run right.
     
  7. fortcollinsram

    fortcollinsram 1/2 ton status

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    [ QUOTE ]
    My yellow wire hooks into a mystery black-box (a little fatter than a cigarrette pack) above the accel. pedal as part of about a 12-pin connector. I also have a pink wire with a black stripe that ties into the fuse block and the cruise wire on the steering column. The black wire.... that will take some more research.


    [/ QUOTE ]



    /forums/images/graemlins/thinking.gifhummmm...IS that black box part of the cruise? I dunnnnoo....You didn't mention the brown wire....I just wanna be sure that that is the wire where the ECM gets it reference signal for the VSS....

    Chris
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    One "plug" is for cruise control, one is for the ECM. Can't recall which.

    Still don't believe TBI trucks didn't get VSS, how did they control IAC? Every other GM TBI application used it.
     
  9. fortcollinsram

    fortcollinsram 1/2 ton status

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    Well I know that my truck HAD VSS...I am just now getting around to hooking it back up (I got rid of the stock speedo that was used as the orgin fo the VSS signal)

    Chris
     
  10. u2slow

    u2slow 1/2 ton status

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    I went out to my parts bunker tonight and dug out an '89 R3500 complete wiring harnes... you know, the one I swore up and down did not have a speed buffer? /forums/images/graemlins/deal.gif

    It has a speed buffer /forums/images/graemlins/eek.gif

    It also has a brown wire /forums/images/graemlins/eek.gif

    I pulled out my multimeter /forums/images/graemlins/eek.gif

    The brown wire traces thru to pin 10 on the "A" side of the 24-pin connector for the ECM.

    Next time, I'll check my junk before I open my mouth and claim expertise on the matter /forums/images/graemlins/blush.gif /forums/images/graemlins/blush.gif /forums/images/graemlins/blush.gif /forums/images/graemlins/blush.gif
     
  11. dyeager535

    dyeager535 1 ton status Premium Member

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    So it sounds like the one wire "pin" on the buffer is ECM feed.

    Not running cruise on my truck (at this point) so I'm not up on which is which. Quite a few variations of the buffer connectors based on year/application. (at least 3 different ones)

    Earlier trucks had TCC and Cruise controlled out of the black box over the gas pedal, but I would be surprised if TCC wasn't controlled by the ECM after fuel injection. Cruise probably stayed over the gas pedal until the very end.
     
  12. fortcollinsram

    fortcollinsram 1/2 ton status

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    Thaks for checkin that Kevin...Now...Where can I get thoese adapters that plug in that t-case and the speedo cable plugs into the adapter and the adapter send the signal to the ECM? I think it was like jagsthatrun or somthing, but wasn't there another place too?

    Chris
     
  13. 88streetblaze

    88streetblaze 1/2 ton status

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    Location:
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    just about anywhere that sells FI stuff,

    painless performance,
    street & performance,
    etc.
     

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