diff --git a/frontend/src/components/DynamicComponent.tsx b/frontend/src/components/DynamicComponent.tsx
index 58ecb4ac..19d0952f 100644
--- a/frontend/src/components/DynamicComponent.tsx
+++ b/frontend/src/components/DynamicComponent.tsx
@@ -552,8 +552,15 @@ export function createComponentFromMetadata(
   y: number;
   properties: Record<string, any>;
 } {
+  // Underscore separators (not '-') so the resulting id is safe to embed
+  // in SPICE component / source names. ngspice's WASM build truncates
+  // vector keys at '-', which broke branch-current lookups for any LED /
+  // ammeter wired up by the user (visible symptom: correct node voltage,
+  // dark LED). Also strip '-' from metadata.id (e.g. 'led-bar-graph') so
+  // the prefix doesn't reintroduce a hyphen.
+  const safePrefix = metadata.id.replace(/-/g, '_');
   return {
-    id: `${metadata.id}-${Date.now()}-${Math.random().toString(36).substr(2, 9)}`,
+    id: `${safePrefix}_${Date.now()}_${Math.random().toString(36).substr(2, 9)}`,
     metadataId: metadata.id,
     x,
     y,
diff --git a/frontend/src/store/useSimulatorStore.ts b/frontend/src/store/useSimulatorStore.ts
index 995eb131..8999f063 100644
--- a/frontend/src/store/useSimulatorStore.ts
+++ b/frontend/src/store/useSimulatorStore.ts
@@ -1894,16 +1894,22 @@ export const useSimulatorStore = create<SimulatorState>((set, get) => {
     // short forward-biased between 5V and GND — real hardware blows the
     // diode, and the ngspice solver returns an indeterminate / NaN branch
     // current so the visual LED never lights up on the canvas either.
+    // NOTE: component ids must NOT contain hyphens. ngspice (WASM build)
+    // truncates branch-current vector names at '-', so a sense source
+    // named V_led-builtin_sense yields the wrong key in branchCurrents
+    // and the LED's update() loop never sees the diode current — the
+    // node voltage is correct (the user sees ~1.84V on the wire) but the
+    // visual brightness stays at zero. Underscore is safe.
     components: [
       {
-        id: 'led-builtin',
+        id: 'led_builtin',
         metadataId: 'led',
         x: 380,
         y: 100,
         properties: { color: 'red' },
       },
       {
-        id: 'r-builtin',
+        id: 'r_builtin',
         metadataId: 'resistor',
         x: 240,
         y: 130,
@@ -1914,24 +1920,24 @@ export const useSimulatorStore = create<SimulatorState>((set, get) => {
     wires: [
       // Pin 13 → resistor pin 1 (current-limiting side).
       {
-        id: 'wire-builtin-pin13',
+        id: 'wire_builtin_pin13',
         start: { componentId: 'arduino-uno', pinName: '13', x: 0, y: 0 },
-        end: { componentId: 'r-builtin', pinName: '1', x: 0, y: 0 },
+        end: { componentId: 'r_builtin', pinName: '1', x: 0, y: 0 },
         waypoints: [],
         color: '#22c55e',
       },
       // Resistor pin 2 → LED anode.
       {
-        id: 'wire-builtin-anode',
-        start: { componentId: 'r-builtin', pinName: '2', x: 0, y: 0 },
-        end: { componentId: 'led-builtin', pinName: 'A', x: 0, y: 0 },
+        id: 'wire_builtin_anode',
+        start: { componentId: 'r_builtin', pinName: '2', x: 0, y: 0 },
+        end: { componentId: 'led_builtin', pinName: 'A', x: 0, y: 0 },
         waypoints: [],
         color: '#22c55e',
       },
       // LED cathode → GND.
       {
-        id: 'wire-builtin-cathode',
-        start: { componentId: 'led-builtin', pinName: 'C', x: 0, y: 0 },
+        id: 'wire_builtin_cathode',
+        start: { componentId: 'led_builtin', pinName: 'C', x: 0, y: 0 },
         end: { componentId: 'arduino-uno', pinName: 'GND.1', x: 0, y: 0 },
         waypoints: [],
         color: '#000000',