1999 NP241C wiring

Discussion in 'Transfer Cases' started by Kbirdjr, Nov 9, 2018.

  1. Kbirdjr

    Kbirdjr Newbie

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    I have a 1999 K2500 (OBS) that I recently swaped an 8.1L i to. The engine came out of a 2001 Silverado (NBS). I retained the 4L80E/NP241C that was already in my truck. I was fortunate enough (I think) to located a wiring harness from a 2001 C3500 (OBS) which of course was 2wd. Everything plugs in just like it was made for this truck and engine combo except the transmission/transfer case. The last thing I need to figure out is how to wire the 4wd transmission and transfer case. The C3500 harness has plugs for the Neutral Safety Switch on the side of the transmission but I have one remaining 4 wire plug that I have not yet figured out. The 4 wires on the truck side one goes to a sensor on top of the transfer case (I think range selector), two go to the 4wd actuator up front, and the 4th i have not been able to track down.

    Are there any transmission/transfer case experts in the group or anyone who can point me in the direction of a good wiring diagram? I have traced the wires through the old 454 harness and they terminate as follows;

    Pin A - goes to pin #23 in black ecm connection (old harness)
    Pins B&C - both black wires, appear to be ground. One ties into another ground wire about half way up the harness and the other goes to the plug on the firewall and connects to D6. Unfortunately I don't know which one is goes where.
    Pin D - Also goes to firewall plug pin E5.

    Any help would be greatly appreciated.
     
  2. Kbirdjr

    Kbirdjr Newbie

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    Can't figure out how to edit my original post so updating here. I have the transmission wiring figured out but I still can't figure out the transfer case wiring. I removed the harness that plugs into the transfer case hi/low switch (3 wires) and the actuator on the front axle (4 wires). There is another third plug (4 wires) that plugged into the old main wiring harness that has now been removed. Below is an update now that I can see it.

    Below i am referring to the large flat 4 wire plug that plugged into the old harness. I need to figure out where to connect each to the new harness.
    Pin A - goes to pin #23 in black ecm connection (old harness) UPDATE - this is a gray/black wire that goes to the center pin on the hi/low switch. I believe this needs to go to pin#13 in the red connector in 0411 ECM.

    Pin B - black wire going directly actuator plug on front axle. I don't know where this should go on the new harness.
    Pic C - black wire that is spliced into a wire going directly to actuator AND to pin A in hi/low plug.

    Both black wires were connected to separate black wires further up the harness. One of them goes to D6 in the main plug on the firewall. It seems that they are both grounds but under different circumstances. Maybe one is getting a ground to control the actuator and the other is sending a signal back to the ECM? I need to know what each should be connected to.

    Pin D - Brown wire. Goes from actuator plug to pin E5 in main plug at firewall. Need to know what this is for.

    If anyone has wiring diagrams for this i would be very appreciative.
     

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