https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2612305153

1. Do you mean livery, or a texture for some interior parts, like dials?
2. You need to position AND orient the door pivots properly. See how pivots oriented relatively to the desired axis or rotation in the model examples, supplied by the devs. Set your pivots accordingly. Also, make sure, you don't have mirrored pivots.
It would be also a good idea to position and orient pivots of all other parts in a fashion, similar to the examples.

correction: "desired axis of rotation"

Originally posted by SaQSoN:

1. Do you mean livery, or a texture for some interior parts, like dials?

Engine textures.

Originally posted by TheCarGuy:

Originally posted by SaQSoN:

1. Do you mean livery, or a texture for some interior parts, like dials?

Engine textures.

Correction: I have a custom part that looks like a Ferrari engine that goes over the real engine.

In this case, you add it just the same way, you add the dashboard instruments texture: in the 3D software, where you make your car, make a material with some destinctive name (include your car name in it, for instance), so it most definitely won't co-inside with other in-game mats, add your texture to the diffuse channel of this mat (the texture should be PNG format), prefferbaly, that your texture name would be the same, as the material name. And apply this material to the polygons, you want to have this texture on.
When exporting, make sure, your PNG texture is stored in Textures folder of your prepared for export model in the Unity. The unity will automatically pick it up. You can check, if it did in the Unity 3D view by dragging there your model. Also make sure to untick "receive decals" checkbox in the materials with textures.
Export you model from Unity into the game format, using the supplied exporter tools, and then make sure, your PNG texture is stored in the root folder of your car.
Make a not, however, that you can not control metlaness and roughness of your material with the texture (it is, probably, possible, but the texture should be prepared with normal, metlaness and other channels and the material should be set up correctly, but you will need to study, how to do it in a unity docs).

Ok, I'll try that.

In unity, my material just shows as the default grey ball, how do change the texture of the material?

1. Did you assign the texture to the diffuse channel of your material in your 3D programm (3D Max, Rino, or whatever you are using to build the model)?
2. If yoiu did (1), make sure, your software exports materials into FBX (majority of 3D proggys do it by default, but may be, the one you are using - does not).
3. If (2) is ok, make sure, you copied your PNG file with the texture into the Textures folders of your prepared car model in Unity project. This folder should be in the same directory, where your model.fbx is copied.
4. If it still does not help, in Unity interface, open the material in question in the Inspector, in the Surface Inputs tab find entry "surface map" and drag&drop your texture.png file onto the little square. That should do it.

Originally posted by SaQSoN:

1. Did you assign the texture to the diffuse channel of your material in your 3D programm (3D Max, Rino, or whatever you are using to build the model)?
2. If yoiu did (1), make sure, your software exports materials into FBX (majority of 3D proggys do it by default, but may be, the one you are using - does not).
3. If (2) is ok, make sure, you copied your PNG file with the texture into the Textures folders of your prepared car model in Unity project. This folder should be in the same directory, where your model.fbx is copied.
4. If it still does not help, in Unity interface, open the material in question in the Inspector, in the Surface Inputs tab find entry "surface map" and drag&drop your texture.png file onto the little square. That should do it.

Thank you! #4 helped a lot!

I wonder, if it will work in-game for you. I mean, additional textures (above the dial texture) and custom textured materials.

Originally posted by SaQSoN:

I wonder, if it will work in-game for you. I mean, additional textures (above the dial texture) and custom textured materials.

I got some interior textures working, and the engine textures too. I have a question. I'm quite stumped about the door axis thing. Is it something I need to do in Blender or Unity?

You should do it in Blender, before you export into FBX.

Originally posted by SaQSoN:

You should do it in Blender, before you export into FBX.

Just wondering, when making your F-50 mod, what did you have to edit to get the doors working correctly?

I didn't have to edit anything, I just built them correctly from the beginning. :-)
Seriously, though, all you need to do is to place and orient pivots for all the body parts correctly. If you are not sure, what "correctly" means (as I was in my time), you can always look at the model examples, found in modding tools folder, that came with the game and just do yours by analogy.
If you are not sure what "object pivot" is and how to modify it - you need to consult your 3D modeling software manual/tutorials.