Lead with the separate-ground LED build

Keeps the shared-rail version documented as the alternative, since that is
what the current loom attempts, and links the new pinout reference.

docs/WIRING.md

@@ -2,6 +2,8 @@
 
 ![Wiring pinout](wiring.svg)
 
+Pin availability and limits: [ESP32-PINOUT.md](ESP32-PINOUT.md).
+
 ## Board to board
 
 | Board A (esp32_bluepad32) | | Board B (esp32 2.0.17) |
@@ -15,9 +17,34 @@ TX goes to RX, not TX to TX. The ground is a shared voltage reference so the
 two boards agree on what a logic 1 is — without it you get garbage or silence.
 It is not a return path for anything else, so do not hang LED current off it.
 
-## LED circuits
+## LED circuits — recommended build
 
-Both live entirely on **board B**. Each is its own complete loop:
+Each LED gets its own wire out and its own wire back to its own GND pin. Four
+wires, no shared junction anywhere.
+
+![LED wiring with separate grounds](wiring-leds-separate.svg)
+
+```
+GPIO25 ──[220Ω]──▶|── RED pair ──── GND (a)
+GPIO26 ──[100Ω]──▶|── GREEN pair ── GND (b)
+```
+
+GND (a) and GND (b) are different physical pins but the same net inside the
+board. That is fine, and it is exactly what makes this safe: there is no shared
+connection point to wire incorrectly.
+
+Both circuits live entirely on **board B**. LED long leg (anode) faces the
+resistor and GPIO side. A reversed LED simply stays dark, so it looks like a
+dead circuit rather than a wiring error.
+
+Resistor values are a starting point: roughly 220Ω for red, 100Ω for blue or
+white. A pin is comfortable at about 12mA and hard-limited near 40mA. If a pair
+draws more than ~20mA — which pre-wired "3V" LEDs sized for a coin cell often
+do — drive it through a small NPN transistor or MOSFET instead of off the pin.
+
+## Shared ground rail — the other way
+
+Also valid, one wire fewer, but it has a junction that can be wired wrong:
 
 ```
 GPIO25 ──[220Ω]──▶|── RED pair ────┐
@@ -25,13 +52,9 @@ GPIO25 ──[220Ω]──▶|── RED pair ────┐
 GPIO26 ──[100Ω]──▶|── GREEN pair ──┘
 ```
 
-The two returns meet **only at the ground rail**, and the rail goes straight to
+The two returns must meet **only at the ground rail**, and the rail goes
-a GND pin on board B. LED long leg (anode) faces the resistor and GPIO side.
+straight to a GND pin. See the failure mode below for what happens when that
-
+junction lands in the wrong place.
-Resistor values are a starting point: roughly 220Ω for red, 100Ω for blue or
-white. A pin is comfortable at about 12mA and hard-limited near 40mA. If a pair
-draws more than ~20mA — which pre-wired "3V" LEDs sized for a coin cell often
-do — drive it through a small NPN transistor or MOSFET instead of off the pin.
 
 ## Known failure mode: LEDs wired in series
 
@@ -57,12 +80,8 @@ identifies it as wiring.
 It must read 0V. Press Circle and measure again — if it rises above 0V, that
 wire is not ground.
 
-**Simplest fix:** give each LED its own separate wire back to its own GND pin
+**Fix:** switch to the separate-ground build above. It removes the junction
-on board B, with no shared return at all. Board B has several grounds, all
+entirely, so this cannot recur.
-common internally. Slightly less tidy, and it removes the junction entirely.
-
-Worth checking polarity at the same time. A reversed LED simply stays dark, so
-it looks like a dead circuit rather than a wiring error.
 
 ---