Textures are assigned through the material editor, assuming this is an unpacked mod sitting inside it's dev mode folder. There might be other previous steps you need to take but you'll need to give more detail as to what you're trying to do - for starters, are you modifying existing content, or is this your own mod you're making?
You have to do that in 3DSMax (that you are using, as i remember it) with the Unwrap UVW Modifier for Example. The easiest Way, with the best "Overview" is, that you select the Polys to that you want to Map the Texture in the Polygon Sublevel (select it by Material) and then add the Unwrap UVW Modifier. In that Way, only the selected Polys are shown and you can map them in the usual Way. If you maybe don't know how to use the Unwrap UVW Modifier, there are a lot of Videos about it on Youtube.
when I apply a material (material editor) on a part in 3ds max on perspective the surface is black while in the showroom of rfactor 2 the requested material appears well What is happening ?
I mean to remember, that we talked about that some Time ago already, but i can not find it anymore. Ensure that you use a Texture that 3DSMax can handle, like old Format DDS and click the Button "Show Shaded Material in Viewport" in the Texture Selection Screen in the Material Editor (Screenshot) 1 or 2 Times, until the Texture appears.
I created several pieces with gmotors texture but suddenly I have the massage below that appears, what is happening?
For all your "Pieces with gmotor Textures", do you use a Multi/Sub-Object Material as main Material and gmotor Materials as its Sub Materials? That is necessary to get everything working properly. Didn't we talk about that in the Past already?
@elec86 if you want visual textures in max, you have to use "standin" in tga format etc. and the switch them in moddev, since 3ds max cant show dds in viewport. From guide: "Default Textures These materials are setup with default textures that are included in Commonmaps. You can download them here should you wish to put them in a search path that max uses. Note, that 3ds Max can't read the DDS files in BC5 and BC7 encoding. You will need to link up to the TGA equivelant." https://docs.studio-397.com/developers-guide/development-tools/3ds-max-material-library
@ThomasJohansen May i correct it a little bit? "since 3ds max cant show dds in viewport" is not fully true. It just can not show the new Format DDS Textures And the Problem is not a new Format Texture in this Case, because, when i remember it right, you already get an Error when you try to select a new Format DDS in the Material Texture Slot. But his Error Message appears when he wants to export the gmt. So is suppose, i is a wrong setup Material "Scheme", as i've said in my above Post.
depending on the object that I import (CAD inventor) some accept the gmotors texture and not others What is happening ?
Can you upload a 3DSMax Scene File where it happens, send me the Download Link by a private Conversation or by Mail and tell me which Parts exactly don't accept a gmotor Material?