I recently modified a nif file from an existing mod (the door to the TARDIS mod, to be exact), to use a different texture (one that includes the St John Ambulance badge restore in the most recent season of Doctor Who), but now the model looks exactly the same regardless of the lighting conditions, any suggestions on how to fix this?

Hard to say for sure, but it sounds like a normal map issue rather than a model issue. Every texture should have a normal map, the normal map is what allows light to illuminate a texture, without it, the texture will stay the same regardless of lighting. If you do have a normal map, be certain it is named simply and matches the texture name. So if your texture is called TARDISdoor.dds your normal should be called TARDISdoor_n.dds and if they don't match this way it will be as if you have no normal. Using underscores or other symbols in texture or normal map names can cause confusion as well so avoid using them. That's my best guess at this point, good luck :foodndrink: