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Old 05-12-2022, 06:22 PM   #1
DjS71
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Join Date: Feb 2009
Location: Santa Rosa, CA
Posts: 267
Wiring Help - Circuit 1020

Hey gang. Finally... almost there. Long story short, my harness is ill put together. I already had to relocate 7 pins on the PCM connector (4 injectors swapped, wires for TPS, MAF & ALT in the wrong place). but now it starts, no codes when last I checked.

Went to put in in gear for the first time the other day, with dreams of putting it on the trailer to the exhaust shop, and.... nothing.

Checked out the Connector @ the 4L80 and everything is where its supposed to be. Checked the corresponding pins in the PCM connector and everything is there except for pin 75 on the blue connector. Turns out this is part of circuit 1020, one of two key on hot / start hot circuits, this one specifically for powering the transmission solenoids on Pin E of the 4l80 connector.

So, this leads me to believe that the guy who did my harness must have spliced in it somewhere. Maybe with the rest of the pinks that are only key on hot. I think the only thing to do is to pull the whole harness back through the firewall and see where the wire from Pin E ends up.

I'm having a hard time deciphering how to fix this when I find it. Is it a Pin 75 to Pin E straight line or do I need to tie it in somewhere along the way. Spent so much time trying to figure it out, I can't trust my own crossed eyes.
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1971 C10 Short/Fleet 307-2BBL/3OTT
1999 Silverado 2500 ECSB 6.0/4L80
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