diff --git a/HARDWARE.md b/HARDWARE.md
index 4bc900a..258389a 100644
--- a/HARDWARE.md
+++ b/HARDWARE.md
@@ -39,6 +39,14 @@ Unknowns are marked `TBD` instead of guessed.
 - Raspberry Pi drives each relay channel independently.
 - Thermocouple boards are connected to Pi GPIO.
 
+## GPIO Wiring (User-Confirmed)
+- Thermocouple channel 1 GPIO lines: `GPIO 5`, `GPIO 8`, `GPIO 7`.
+- Thermocouple channel 2 GPIO lines: `GPIO 11`, `GPIO 12`, `GPIO 13`.
+- Channel 2 thermocouple mapping corresponds line-for-line to channel 1 mapping (`5/8/7` -> `11/12/13`).
+- Relay control (channel 2): `GPIO 9`.
+- `TBD`: confirm relay control GPIO for channel 1 in this dual-channel prototype wiring doc.
+- Note: these dual-channel GPIO assignments differ from the current single-channel `piNail2/config.json` runtime pins.
+
 ## Monitor Subsystem
 - Separate 12V power supply for the built-in monitor.
 - Short HDMI from Pi -> monitor.