Model loads completely black with no visible material

• The silhouette is visible, proving the geometry is in the scene, but every face is pure black.
• Rotating the model does not change brightness at all.
• No WebGLRenderer errors appear and the materials are MeshStandardMaterial.

1. Swap the material for MeshBasicMaterial: if it becomes visible, lighting is the cause.
2. Count the lights with scene.children.filter(o => o.isLight).length.
3. Check that renderer.outputColorSpace is THREE.SRGBColorSpace.
4. Check whether material.color was overwritten with 0x000000.
5. Check whether part of the meshes use KHR_materials_unlit.

Add a HemisphereLight with 0xffffff, 0x444444 and intensity 1.5 plus a DirectionalLight at intensity 2.0 positioned at 50, 80, 30, and set outputColorSpace to SRGBColorSpace with ACESFilmicToneMapping. Mark colour maps only with map.colorSpace = SRGBColorSpace.

gltf.scene.traverse(function (o) {
  if (o.isMesh) {
    console.log(o.name, o.material.type, o.material.color.getHexString());
  }
});

var renderer = new THREE.WebGLRenderer({ antialias: true });
renderer.setSize(window.innerWidth, window.innerHeight);
renderer.outputColorSpace = THREE.SRGBColorSpace;
renderer.toneMapping = THREE.ACESFilmicToneMapping;
renderer.toneMappingExposure = 1.0;

var scene = new THREE.Scene();
scene.background = new THREE.Color(0x1b1f24);

var hemi = new THREE.HemisphereLight(0xffffff, 0x444444, 1.5);
scene.add(hemi);

var dir = new THREE.DirectionalLight(0xffffff, 2.0);
dir.position.set(50, 80, 30);
scene.add(dir);

var loader = new THREE.GLTFLoader();
loader.load('/models/pump.glb', function (gltf) {
  scene.add(gltf.scene);
  renderer.render(scene, camera);
});

• Setting map.colorSpace to SRGBColorSpace on normal or roughness maps, which must stay linear.
• Raising light intensity to 10 to counter the darkness instead of adding a directional light, which flattens all shading.