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I am doing a swap on 2005 Chevy Silverado 1500 with 4.3 and nv3500 to 5.3 l59 out of 2003 tahoe but swapped the harness to blue green connector harness and got everything connected in fuse box but happen to have two extra connector coming from the body harness that run along the drive side and up to fuse box. that the engine harness doesn’t have. 1 single blue wire connector. 1. 3 pin connector shown in the photos if anyone could help not sure if they’re needed
older post about swapping
a long read...you might find the info you are looking for there.
Are the wires you are looking to connect on the v8 harness or the truck harness?
I found out from reading a few it’s connector c153. which is for the front axel and 4wd. I ended up using my v6 harness as to know where it goes because it Already had that connector. All the wires go to green connector except the brown one. pin 16 is grey/black. pin19 is black/white which has two same color that run to ecu and to c2 connector to B3 which is Axle Switch Signal. Brown wire runs to C100 conector under fuse to ignition 3 voltage. Not sure it that helps anyone but I couldn’t really find anything on the connector
im still unsure of blue single wire which runs I think to the back of truck maybe taillights or something?
I found out from reading a few it’s connector c153. which is for the front axel and 4wd. I ended up using my v6 harness as to know where it goes because it Already had that connector. All the wires go to green connector except the brown one. pin 16 is grey/black. pin19 is black/white which has two same color that run to ecu and to c2 connector to B3 which is Axle Switch Signal. Brown wire runs to C100 conector under fuse to ignition 3 voltage. Not sure it that helps anyone but I couldn’t really find anything on the connector
im still unsure of blue single wire which runs I think to the back of truck maybe taillights or something?
That single blue wire doesn't actually have anything connected to it. It's supposed to be to prime the fuel pump (I can't recall if you ground it or apply 12V+?). I've never actually tried it. But my GMT800 trucks have that and the connector just hangs there.
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4.3 v6 to 5.3 ls missing connector? 
