How do you integrate a Holley Terminator X Max while keeping the factory ECM, gauges, and A/C in an '03-'07 Silverado?

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

Other wiring

• Holley Terminator X; GM LS: Holley Terminator X provides an A/C Kick input on ECU pin A12 (connector pin A, white/blue) and an A/C Shutdown output on ECU pin B10 (connector pin G, gray/black) that deactivates the clutch at a configured throttle position; the kick input is a ground-activated signal. (Holley (via CARiD mirror))
• Holley Terminator X; GM LS: Holley Terminator X has an IAC Kick feature that automatically adds IAC steps so the engine does not experience a momentary drop in idle when the A/C compressor kicks on. (Holley (via CARiD mirror))
• Holley Terminator X; GM LS: The Current Performance Holley Terminator A/C integration module operates the A/C compressor clutch, interfaces with the Holley ECU for A/C shutdown and IAC kick, and signals the ECU to request electric fan operation while the A/C runs; it includes binary pressure-switch leads, an A/C relay, and a 10-amp inline fuse. (Current Performance Wiring)

Transmission control

• Holley kit 550-916 supports 24x LS1/LS6 engines with EV1 injectors and includes electronic transmission control for 4L60E/4L80E with a transmission-control harness in the box. (Holley)

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