GM Wiring Harness (octopus)

Discussion in 'Injection Tech' started by Bill USN-1, Nov 8, 2005.

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  1. Bill USN-1

    Bill USN-1 Moderator Staff Member Moderator

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    OK, I will go pin by pin on the 1227747 harness.
    FIRST- You will NEED the set of diagrams available from here
    Or attached below.
    There is also a very nice 1 page pdf file in this thread!
    There are 2 connectors. If you look really close you can see they are labeled. The small one is A & B. The large one is C & D.
    There are also numbers on the plug for each pin.
    Some basics:
    I run 2 relays. 1 for 12v to the ignition, ECM power and injectors, and 1 for the fuel pump. I use the basic 30 amp aux lighting relays from the parts store. If the harness came with the factory fuel pump relay than I retain that relay. If not I use the 2nd 30 amp relay for the fuel pump. Both relays are energized from the 12v ignition wire that used to go to the + side of the coil. Since it is only used to turn the relays on there is less draw on the stock 30 year old scout wiring.
    I don't run the ign from the switch. Due to voltage drop from the old IH wiring. I run all switched(from the key "on" position) 12vdc thru the relay.

    If you use a bosch style relay here are the pins:
    There are several different versions of the relay out there so look at the pin numbers before you buy one.

    30-12v fused input(should also hook up your org ECM constant 12v to this wire)
    85- Gnd
    86- 12vdc from ign sw(black wire that was hooked up to the coil + or grn/wht from ECM for fuel pump )
    87- pink/blk, pink(ignition, ecm power)
    87- red, white(injectors)

    there are 2- 87 output terminals on the SPST 5 terminal relay so you can use both. For a SPDT there is 1-87 and 1-87a. See the diagrams. They are opposite in operation and can not be interchanged. If you wire to 87a your circuit will be on all the time with the key off and then be off with the key on.

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    Using factory fuel pump relays....


    To start with go to this link and get the diagrams.
    You want to get sheet 2 and 3.
    At the bottom of sheet 2 is the FP relay circuit for the S/T M series of trucks.
    I will use it for the explaination.
    Here's the diagrams...they are also attached below.
    diagrams


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    Note:
    Pin A comes from the ECM pin A1 and is used to apply 12V to the relay to turn it on.

    Pin C is the ground wire. Can be connected to one of the black/wht wires.

    Pin D is your 12V from a fuse. This is normally tied to the org wires B1 and C16. It is the same that provides the bat 12V to the ECM.

    Pin B is the output of the relay going to the Fuel Pump or any other load you have connected to it.
    This also ties to pin B2 of the ECM to tell it when the FP is actually running.


    Now the pin letters may not be exactly the same as this diagram. That's not important. It you follow the diagram here and the description and just match it up to the diagram on your relay!!!
    Here is a modified diagram (sheet 2 attached at bottom of post) showing one of the alternate pin designations on the relay and also shows the removal of the oil pressure switch.

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    Some additional info.Painless wiring install guide

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    Attached Files:

    Last edited: Apr 8, 2014
  2. Bill USN-1

    Bill USN-1 Moderator Staff Member Moderator

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    Here's the rest of the diagrams.
    Attached below is a voltage check spreadsheet from CaverDave(with a few updates) for you to log your voltage checks prior to hitting the key!!
    The 1 sheet color wiring diagram is also attached.
     

    Attached Files:

    Last edited: Dec 11, 2013
  3. Bill USN-1

    Bill USN-1 Moderator Staff Member Moderator

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    More diagrams.

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