Re-pinning a 4L60E harness for a 4L80E
You can re-pin the factory harness instead of buying a new one. On a 1999–2007 Gen III truck or LS1-style harness it's five wire moves plus a new 2-pin pigtail for the 4L80E's input speed sensor:
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| Where | Wire | Was (4L60E) | Becomes (4L80E) |
|---|---|---|---|
| Round trans connector, cavity S | White | 3-2 shift solenoid | Pull it out; reuse it for the input speed sensor |
| Round trans connector, cavity T | Tan/black | Converter clutch on/off | Pull it out; reuse it for the input speed sensor |
| Round trans connector, cavity U | Brown | Converter clutch PWM | Move it to cavity S (the 4L80E converter clutch) |
| PCM C1 (blue), pin 79 | White | 3-2 shift solenoid | Move to C2 (red or green) pin 22, input speed sensor high |
| PCM C2 (red or green), pin 42 | Tan/black | Converter clutch on/off | Move to C2 pin 23, input speed sensor low |
| New 2-pin pigtail | White + tan/black | — | Plugs into the input speed sensor on the 4L80E case |
Seal the empty T and U cavities in the trans connector. Red-connector (1999–2002) and green-connector (2003–2007) computers use the same pin numbers for this job. Check your wire colors against our P01/P59 pinout before you move anything.
The computer also has to be set up for a 4L80E (a segment swap on a P01/P59), and the converter clutch needs a working two-position brake switch input. Mechanical side and the rest of the checklist: 4L60E to 4L80E steps.
You can re-pin the existing harness instead of buying a new one. The 4L60E connector has 13 wires and the 4L80E connector has 11: pull pins S (white) and U (brown) at the transmission connector, move the brown wire to the S position, and leave the white one disconnected. Then wire the 4L80E's extra input speed sensor to pins 22 and 23 of the PCM's red connector (pin 22 to sensor pin A, pin 23 to sensor pin B), or pins 22/23 of the green connector on newer blue/green PCM trucks. We've seen this work on a 2000 model.
Check this first:
- Check whether your PCM uses the red connector or the newer blue/green connectors
- Confirm the wire colors at pins S and U before moving anything
- The PCM tune must also be set up for a 4L80E
Based on what we've seen work across our own builds, our friends' builds and the wider LS community, reviewed by our lead shop tuner (over 20 years of LS and LT tuning experience). Every combination is different, so use at your own risk and check our safe tuning limits before any wide-open pass.
Go deeper
Every option we know of
| Maker / product | Part # | Fits | Price | Where | Status / notes |
|---|---|---|---|---|---|
| Sloppy Mechanics (community) PCM removal write-up (Sloppy Mechanics Wiki) | n/a | TBI-truck LS swaps | Free | sloppymechanics wiki | Online Community doc; cross-check with a second source |
| LT1Swap Wiring diagrams and pinouts | n/a | Gen III harnesses | Free diagrams | Online Match diagrams to your exact ECM | |
| BP Automotive Standalone harness (skip the removal entirely) | varies | Clean-sheet swap wiring | about $800-1,200 | bp-automotive.com | Built to order One-person shop |
Prices are approximate as of September 2026. We list every option we know of, including small shops and used parts we can't link to. Confirm fitment with the seller.