How do you wire a DIY e-fan harness on a 99-02 truck, and what PCM pins trigger the relays?

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

Harness and power

• E38 ECM; Chevrolet Performance NA LS control kit 19171935; LS2/LS3/LS376/LS7/LSX454; 58x/4x; 2006+: ECM-controlled fan output turns on at 97 C (207 F). (Chevrolet Performance)
• E67 ECM; Chevrolet Performance LSA E-Rod control system 19299067; LSA: LSA fan requires vehicle speed before it turns off after activation. (Chevrolet Performance)
• 0411 PCM (GM service #9354896 or 12200411); 1999-2007 Vortec DBC (LM4/LM7/LQ4/LQ9/L33/L59); T56 or non-electronic automatic: Fan trigger wires are ground-side controls for customer relays. (PSI Conversion)
• 0411 PCM (GM service #9354896 or 12200411); 1999-2007 Vortec DBC (LM4/LM7/LQ4/LQ9/L33/L59); T56 or non-electronic automatic: Fan on/off temperatures differ between stock and PSI calibrations. (PSI Conversion)
• Sources differ: Chevrolet Performance E38 kit fan-on at 207 F (different controller/calibration)
• E38 ECM; Aeroflow AF49-1506; 58x LS3/LSX; DBW; T56 or non-electronic automatic; 2006+: AF49-1506 stock fan temperatures; one relay per fan. (Aeroflow Performance)
• Gen III PCM; Aeroflow AF49-1505; LS1/LS6; DBC; 4L60E/4L80E: Fans that stay running indicate a missing CEL or stored trouble codes. (Aeroflow Performance)
• E38/E67 ECM; Speartech 58x manual-transmission harness: Speartech fan controls are ground triggers to customer relays. (Speartech)

Other wiring

• P01/P59; Gen III LS; 1999-2007: PSI stock PCM calibrations turn Fan 1 ON at 226F and OFF at 221F, and Fan 2 ON at 235F and OFF at 230F; when PSI programs the PCM it sets fan-on points to 195F and 205F. (PSI Conversion / Performance Systems Integration (via SlideShare))
• Sources differ: Fan-on temperatures are calibration-dependent: forum-reported custom tunes commonly use 190/205F, and PSI's own reprogram sets 195/205F rather than the stock 226/221 and 235/230.
• P01/P59; Gen III LS; 1999-2007: PSI standalone harnesses provide a dark-green Fan 1 Ground wire and a dark-blue Fan 2 Ground wire at the PCM connector; each grounds the ground side of the customer's own fan relay. (PSI Conversion / Performance Systems Integration (via SlideShare))

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