Add power wiring guide: LRS-350-12 -> J1000, AC-switch power design

Pinouts sourced from mothenjoyer69/bc250-documentation hardware.md.
Power switch = fused+switched IEC inlet on the AC side, with
AUTO_PWRON1 jumper 1-2 so the board boots when 12V appears.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

README.md

@@ -38,6 +38,8 @@ The ISO installs **unattended** and bakes two users from
   publish OTA updates (verified podman and docker paths, with workarounds)
 - [`OPERATIONS.md`](OPERATIONS.md) — day-2 admin: connecting, installing
   games remotely, updates/rollback, GPU tuning, health checks
+- [`WIRING.md`](WIRING.md) — PSU/mains wiring, J1000 pinout, power-switch
+  design (AC rocker + AUTO_PWRON), fans, first power-on
 
 ## Hardware prerequisites (on the board, not in the image)
 

WIRING.md

@@ -0,0 +1,118 @@
+# BC-250 Console — Power Wiring Guide
+
+Wiring a **Mean Well LRS-350-12** (12 V / 29 A / 350 W) to the BC-250's
+**J1000** PCIe 8-pin power input, with an AC-side power switch.
+
+> ⚠️ **The AC side of this build is mains voltage. It can kill you.**
+> Work with the cord unplugged, never trust a switch to isolate, keep AC
+> terminals covered when done (the LRS-350 ships with a terminal cover —
+> use it), and if you are not comfortable with mains wiring, have someone
+> qualified do §2.
+
+## 1. Parts
+
+| Item | Notes |
+|---|---|
+| Mean Well LRS-350-12 | Screw-terminal PSU: `L`, `N`, `FG` (AC side) + 3× `+V`, 3× `−V` (DC side) |
+| PCIe 8-pin pigtail, 16 AWG | The **female receptacle** end mates with J1000. Must be **PCIe**, not EPS/CPU — the keying differs and EPS swaps 12 V/GND. Never force a connector. |
+| Fused + switched IEC C14 inlet module | The cleanest "power switch": cord socket, rocker, and fuse in one panel part. Rated ≥ 250 VAC / 6 A. Fit a **5 A slow-blow** fuse (PSU pulls ~4 A max at 115 V, half that at 230 V). |
+| Grounded (3-wire) IEC mains cord | Earth is not optional — the PSU chassis and `FG` must be earthed. |
+| Ring or fork crimp terminals + ferrules | For the PSU screw terminals. Bare stranded wire under screws loosens over time. |
+| Heat shrink, zip ties | Insulate every AC joint; strain-relieve everything. |
+| Multimeter | Non-negotiable for §4. |
+
+## 2. AC side (mains → PSU)
+
+```
+ IEC inlet module                          LRS-350-12
+┌───────────────────┐
+│ L ──── FUSE ──── SWITCH ────────────────► L
+│ N ──────────────────────────────────────► N
+│ E (earth) ───────────────────────────┬──► FG (ground symbol)
+└───────────────────┘                  └──► case earth stud (if separate)
+```
+
+- Fuse and switch go in the **Live** line only (a double-pole switch that
+  also breaks N is even better; never switch only N).
+- Insulate the inlet's spade terminals with heat shrink or boots — they're
+  live whenever the cord is plugged in, switch position irrelevant.
+- Earth goes straight through, unswitched and unfused, to `FG`.
+- Fit the PSU's plastic terminal cover after wiring.
+
+## 3. DC side (PSU → J1000)
+
+J1000 pinout (from the BC-250 hardware docs):
+
+```
+[ GND GND GND GND ]      3 × 12 V pins, 5 × GND pins
+[ GND 12V 12V 12V ]
+```
+
+- Run **each of the three 12 V wires to its own `+V` terminal** and the
+  ground wires to the `−V` terminals (bundle grounds 2-per-terminal if the
+  pigtail has five). The LRS-350 has three terminal pairs precisely so you
+  can split high current — at the board's ~220 W TDP that's ~18 A total,
+  ~6 A per 16 AWG wire. Comfortable.
+- Keep the run short — under ~1 m limits voltage drop.
+- Ferrules or ring terminals on every wire; screw them down hard and tug-test.
+- Don't extend or thin the wires: 16 AWG minimum, as delivered.
+- No inline DC fuse needed — the LRS-350 has over-current, over-voltage,
+  and short-circuit protection built in.
+
+## 4. Verification — BEFORE the board ever sees power
+
+With the **pigtail connected to the PSU but NOT to the board**:
+
+1. **Continuity (AC off, cord unplugged):** beep out each connector pin to
+   its PSU terminal. Confirm the three pins on J1000's `12V` positions trace
+   to `+V` and all others to `−V`. Match the pinout above against the actual
+   connector — identify which row is which by following the wires, not by
+   assuming latch orientation.
+2. **Voltage (AC on, board disconnected):** switch on. Measure across the
+   connector's 12 V/GND pins: expect **12.0–12.2 V** (trim with the PSU's
+   `+V ADJ` pot if needed). Then probe **every pin pair** — any 12 V on a
+   pin that maps to GND means STOP and re-check.
+3. Switch off, plug into J1000 (it only seats one way — if it doesn't seat,
+   it's the wrong connector, do not force), then proceed to §5.
+
+## 5. The power switch (how the console turns on and off)
+
+The BC-250 has no case power button — it was a rack blade. Instead:
+
+**`AUTO_PWRON1` jumper → pins 1-2** (factory default; also matches the BIOS
+`AUTO_PWRON` setting from the install checklist). The board now boots
+automatically the moment 12 V appears — so **the rocker on the IEC inlet *is*
+the console's power switch**, exactly like a TV:
+
+| Action | Result |
+|---|---|
+| Rocker ON | PSU powers up → board auto-boots → GNOME login |
+| Shut down from GNOME / `sudo systemctl poweroff` | Board off; PSU still energized (standby). Stays off until AC is cycled. |
+| Rocker OFF → ON | Full power cycle → boots fresh |
+| Rocker OFF | Everything dead. Fine to do after a soft shutdown; the OS is btrfs and the image is atomic, but teach the kid "menu shutdown first" anyway. |
+
+Notes:
+- Jumper position 2-3 instead makes the board wait for a power-button press —
+  useless in a custom case (there's no accessible button; don't use this mode).
+- `J2001`'s `PGD` pin powers the board **off** when shorted to ground — that's
+  a blade-chassis signal, not a power button. Leave J2000/J2001 unconnected.
+- Leave the console rocker-ON overnight sometimes: automatic OS/app updates
+  install while it's powered.
+
+## 6. Fans (they also need 12 V)
+
+- `CPU_FAN1` is a standard 4-pin PWM header: `[ PWM Tach 12V GND ]` — BIOS
+  fan curve applies. Put the primary heatsink fan here.
+- More fans: a PWM splitter on `CPU_FAN1` (fine for 2–3 standard fans), or
+  run extras directly off a spare `+V`/`−V` pair (they'll run full speed,
+  always — crude but effective for case airflow).
+- Don't forget airflow over the **backplate** — the GDDR6 underneath runs
+  hot and has no temperature sensor.
+
+## 7. First power-on
+
+1. J1000 seated, fans connected, DisplayPort to TV, keyboard for BIOS.
+2. Rocker ON. Expect: fans spin, DisplayPort shows POST within ~30 s.
+3. No signs of life in 30 s → rocker OFF, re-do §4. Do not keep retrying.
+4. First stop: BIOS — confirm the firmware/VRAM settings from the install
+   checklist, then boot the installer USB.