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Thread: PRND indicator question...

  1. #1
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    PRND indicator question...

    ok so i have searched and there are a few threads on how to hook it up but i dont fully understand.

    yes i have the swap in and running. everything worked fine from the get go with the starter and tranny as i deleted the wiring from the stock harness and used the plugs from the harness that came with harness from the motor (7pin and 4 pin) obviously my indicator light isnt working as there is no signal going to it.

    my question is, WHAT EXACTLY TELLS THE DASH WHAT LETTER/NUMBER TO DISPLAY? i havnt found anything on the net that explains how the circuit works and i was hoping someone knew and could explain a lil more in detail.

    from what i gather, the signal is from the 4pin connector that goes to the pcm and the pcm then tells the dash what to display. my confusion is that there is only 4 pins.... and there are 7 led's that light to indicate the gear.....

    does the prindle switch send a combination of signals to the pcm which it deciphers and tells which led to illuminate? thats the only way i can see it working. if this is not it please enlighten me!!

    my problem is that i unfortunately cut the wires from the old harness thinking i didnt need them... well if i want the light to work (which i do) i will now have to find them and hook them up somehow. do i just find the 4 wires and "piggy back" them to the LS 4 pin connector and that should make the light work? or is it just one wire i need? or two..etc???

    the other problem is that the escalade diagrams show pin numbers for the pcm but the obs diagrams dont have pin numbers and there are several wires which are the same color.... how to i go about picking the correct wires from the old harness to hook back in? does anyone have a pinout diagram for the obs pcm???

    i opologize for the long post especially if this has been covered but i cant for the life of me find it! it would be great if you could tell me how to hook it up but i would REALLY like to know how the circuitry works if possible. thanks!
    Like Tumbler in "Gone in 60" I'll drive anything with wheels or without

    My 95 ECSB LQ9 build thread - http://www.ls1truck.com/forums/lsx-t...to-95-obs.html
    CALI LEGAL ENGINE SWAP!
    Stock 03 LQ9, DBW, 95' 4l80e w/ Transgo shift kit, 2010 50# GM injectors, 2800 Circle D stall, Spectre CAI, Upgraded trans cooler, Home-made E-fans/shroud, Dual EP-381 fuel pumps w/Home-made hotwire kit
    NEXT ON LIST: Dual Battery setup, CAM/Valvetrain upgrade, Build my own rear mount turbo, TRU-TRAC, HIT THE STRIP!!!

  2. #2
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    anybody?

  3. #3
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    Man I can help you out but I dont have the wiring diagrams with me at work. I just went through all this and the MLPS/ PNP/ PRNDL what every you want to call it has 4 wires that you are well aware of. Signal A,B,C,P and depending on what gear its in the signals will be a combination of voltage or open which tells the display where the gear select is. I will try and hook you up when I get home but you will need to get the wiring/ connector and the switch that goes on the side of the transmission to make it work.
    2010 Silverado 4.8 Ext Cab 4x4
    Cam, Stall, 4.88's

  4. #4
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    Untitled by Badger009er, on Flickr


    Untitled by Badger009er, on Flickr


    Untitled by Badger009er, on Flickr

    Ok So here is what you can do.

    If you found the original connector that goes with the switch and the colors match awesome. If not you will need to check continuity with a multimeter.

    All of my connections went from the A, B, C, P from the main connector in the trans through a homemade pigtail to the MLPS switch on the side of the transmission.

    All the indicators worked except for Park , 2, 1 and according to the first image I posted I had a problem with signal B not getting 12v when it should of. If you have the same problem unplug your main transmission connector and check your PRNDL indicator to see if its reading Park correctly. If so just run you B signal to the switch on the side of the transmission and disconnect it from the 13, 15, or 17 pin round connector going into the valve body.

    Hope this helps you get moving again!
    Last edited by Gus; 08-14-2013 at 09:13 AM.
    2010 Silverado 4.8 Ext Cab 4x4
    Cam, Stall, 4.88's

  5. #5
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    Edmonton, AB, Canada
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    I have the exact opposite problem that Gus had. I spliced the wires from the PNP plug(the 4 wire one) to the c200 connector. I only have Park, 1st and 2nd.
    3rd, OD,N and R do not light up.
    Back Alley Motorsports 98 GMC
    -5.3l LM7 bored to 5.7l Thompson Motorsports -72mm T4 Magnum Turbo
    -TU1 Custom Grind cam(spec speed.inc) -799 heads
    -.660" Trick Flow dual valve springs -Forged Probe Pistons 3.902" flat top

  6. #6
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    wow. thanks for the reply. thats great info. theres alot more to lighting up those stupid lights than you think. now which display are you speaking of? for the 88-98 OBS trucks right? as that is what i have. (95)

    heres my problem.... the original connector, i cut it off.... its gone and im soley using the connectors that come with the LS harness. this is why im kinda screwed because now i dont know which wires they were going to the old computer... there are several of the same color. i have no idea to figure out which one is which due to the fact that the old computer doesnt have pinout numbers/labels. i dont want to be guessing and applying voltages on the wrong wires you know?
    Like Tumbler in "Gone in 60" I'll drive anything with wheels or without

    My 95 ECSB LQ9 build thread - http://www.ls1truck.com/forums/lsx-t...to-95-obs.html
    CALI LEGAL ENGINE SWAP!
    Stock 03 LQ9, DBW, 95' 4l80e w/ Transgo shift kit, 2010 50# GM injectors, 2800 Circle D stall, Spectre CAI, Upgraded trans cooler, Home-made E-fans/shroud, Dual EP-381 fuel pumps w/Home-made hotwire kit
    NEXT ON LIST: Dual Battery setup, CAM/Valvetrain upgrade, Build my own rear mount turbo, TRU-TRAC, HIT THE STRIP!!!

  7. #7
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    Well obviously what i did isnt working properly. But from my understanding the 4 pin connector sends out A, B, C and P signals. Just search PNP plug 4l60e on google for a diagram, and splice those wires to the c200. So you will have them split to the LS ECM and to the c200. Wire colour should match. Hope this is some help. I dont know why my lights dont all work. I unplugged the signal B and Park, 1 and 2 still all work, but according to that diagram of hi and lo signals, nothing should light up.
    Back Alley Motorsports 98 GMC
    -5.3l LM7 bored to 5.7l Thompson Motorsports -72mm T4 Magnum Turbo
    -TU1 Custom Grind cam(spec speed.inc) -799 heads
    -.660" Trick Flow dual valve springs -Forged Probe Pistons 3.902" flat top

  8. #8
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    Mar 2013
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    Edmonton, AB, Canada
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    I talked to Brendan from lt1swap.com and he says the PRNDL is run directly from the tranny and does not run through the ECM on obs trucks. Newer digital ones obviously run through the ECM.
    Back Alley Motorsports 98 GMC
    -5.3l LM7 bored to 5.7l Thompson Motorsports -72mm T4 Magnum Turbo
    -TU1 Custom Grind cam(spec speed.inc) -799 heads
    -.660" Trick Flow dual valve springs -Forged Probe Pistons 3.902" flat top

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