What's the best wiring approach for an LM7 LS swap: stripped stock harness with stock ECM and fuse block, full standalone harness, aftermarket harness with stock ECU, or a standalone ECU?

Here is what the documentation says. Each point links to its source; details depend on your exact computer, harness and transmission.

Computer and tune

• E67; LS2, LS3, LS376, LS7, LSX454; 2006+: Chevrolet Performance's LS control system guide specifies the kit is designed for LS crate engines with 58x crankshaft reluctor wheels, 4x camshaft timing, and electronic throttle control (generally 2006 and newer), and requires a fuel system holding a constant 400 kPa (60 psi) delivering at least 40 gph for LS2/LS3/LS376 or 50 gph for LSX454 and LS7. (Chevrolet Performance (via Scribd))
• P59 1MB; LS1, LS6, LR4, LM7, LQ4, LQ9; 2003-2007: The 2003-2007 1-megabyte Gen III PCMs are identified externally by a green connector replacing the earlier blue connector; service codes include 12576106, 12586243, 12586242, 12583560, 12583561, and 12589463. These units are interchangeable with a complete re-flash of the appropriate operating system and are considered the optimal choice for LS transplants. (GM High-Tech Performance / MotorTrend)

Harness and power

• 0411 PCM (GM service #9354896 or 12200411); 1999-2007 Vortec DBC (LM4/LM7/LQ4/LQ9/L33/L59); T56 or non-electronic automatic: PSI HAR-1019 fits 1999-2007 Vortec DBC with T56 or non-electronic auto. (PSI Conversion)
• 0411 PCM (GM service #9354896 or 12200411); 1999-2007 Vortec DBC (LM4/LM7/LQ4/LQ9/L33/L59); T56 or non-electronic automatic: HAR-1019 deletes EGR, AIR, CCP and rear O2 wiring. (PSI Conversion)
• Gen III DBW: blue/green P59 PCM; Gen III DBC: red/blue 0411 PCM; 1999-2007 Vortec; 4L60E/4L80E: BP Automotive hookup wires: fuel pump, ignition, TCC brake, MIL, speedo, tach, fans, cruise. (BP Automotive)
• Gen III DBW: blue/green P59 PCM; Gen III DBC: red/blue 0411 PCM; 1999-2007 Vortec; 4L60E/4L80E: BP Automotive deletes EGR, AIR, EVAP and rear O2s in standard form. (BP Automotive)
• Howell standalone harness: Howell standalone harness: Bosch relays, fuse block, OBDII port, built-in CEL. (LSX Magazine)
• 1998-2002 Vortec DBC standalone harness: PSI Vortec standalone harness advertises a simple 4-wire hookup. (Speedway Motors)

Confirm against the instructions for your exact parts before wiring. More: Computer and tune in our tuning guide.