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Thread: 05 GTO LS2 engine harness swap help! Please!

  1. #1
    Registered Member

    Join Date
    Sep 2015

    05 GTO LS2 engine harness swap help! Please!

    Hello everybody and thanks in advance for the help. I've got an 05 gto ls2/4l65e engine going into a 79 trans am. I have the ecm, tcm, and gas pedal which is all I'm planning on using, so now I'm labeling the harness wires to get ready to do the modifications. At the moment I have 2 browsers open each with about 10 tabs running trying to find the information on my own, but now I need the help of somebody with more experience than me.
    I've found pinouts for the three computer connectors, connector 206 (c206), and connector 201 (c201), but I'm afraid they don't match up 100%. So can anybody link me or attach the correct 2005 GTO automatic pinouts? Specifically my questions are:

    1) C206 diagram says pin 25 is engine speed signal, but pin 48 on C1 diagram (computer connector) says tach signal?
    2) C206 diagram says pin 1 and 2 not used and shows VSS on pin three, but pin 1 on my connector has high speed data and fuel level sending on pin 2 and no VSS at all on C206, but has VSS at C1 pin 21. (but it appears that all the other wires on this C206 26 plug connector are matching up)
    3) On C1 pin 32 diagram says stop lamp switch signal and C206 pin 3 has stop lamp switch signal which I traced into the TCM. Do I hook up both to the brake light switch? Or is the diagrams that I'm looking at wrong? What about C1 pin 46? Can I ignore that pin?
    4) What is needed at C1 pin 51 (park/neutral position switch)? The car does not, from the factory, have an electric neutral safety switch. It's mechanical. But I have micro switches to fab one in place if needed. I'm just unsure what is needed here. Is there a neutral safety switch at the range selector on the tranny?
    5) C1 diagram says pin 54 not used, but I have a white wire there, which I think could be EVAP control? Any ideas?
    6) Why is C1 pin 19 wire orange ( Ignition voltage 3)? Is that constant hot or keyed hot?
    7) What is accessory voltage? I've seen like 2 or 3 wires labeled that? What's the deal there?
    8) Extended travel brake switch? C1 pin 38.
    9) C1 pin 10 (engine control relay) Is this the signal from the ecm to turn on the fuse block relay that I'll be making?

    I think that's all I'm needing answers to and I know it's a lot and I know the information has been asked a thousand times, but I really have been trying to not bother anybody about it and try to figure it out on my own, but if I'm looking at bad information then I'm dead in the water! So I really need some help from experienced minds.
    To those that will take the time to read this mess and answer some of the questions I really appreciate it as you'll be giving me knowledge. Thank ya'll so much!

  2. #2
    Registered Newbie

    Join Date
    Jun 2015
    I think I have all your answers. Ive been working on this for the last week or so. Here is what I found.

    2005 GTO C 206
    On Engine Wiring Harness White 26 Pin Connector (Manual Transmission T56)
    C-206- Color Function
    Pin 1 Brown Looped to Pin 4 CAN Buss - Not Used
    Pin 2 Black to C3-49 Low Ref
    Pin 3 Open
    Pin 4 Brown Looped to Pin 1 CAN Buss - Not Used
    Pin 5 Brown / Blk Looped to Pin 12 CAN Buss - Not Used
    Pin 6 Open
    Pin 7 Brown / Blue Reverse Light Sensor
    Pin 8 Open
    Pin 9 Open
    Pin 10 Dark Green Goes into the horn connector and then out into the harness as black / red. It continues to the right coils / injectors and ends up at the A/C compressor
    Pin 11 Open
    Pin 12 Brown / Blk Looped to Pin 5 CAN Buss - Not Used
    Pin 13 Pink Merges with other pinks (Ignition 1?)
    Pin 14 Open
    Pin 15 Lt Green / Black to C3-51 A/C Compressor clutch relay control
    Pin 16 Open
    Pin 17 Open
    Pin 18 Open
    Pin 19 Open
    Pin 20 Open
    Pin 21 Yellow Reverse Lock Out
    Pin 22 Lt Green / Black Reverse Light Sensor
    Pin 23 Open
    Pin 24 Open
    Pin 25 Open
    Pin 26 Open

  3. #3
    Registered Member

    Join Date
    Sep 2015
    Hey thanks for that information! So how is your harness coming along? Specifically your E40 C1, C2, and C3 connectors? Have you figured out all your external "car" connections from C1?

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