3D models gets partially black and some mappings looks distorted after applying a SCS' materials

[Ma7heus]

Hello SCS community I need help on those 3 issues with new parts i did for MB MP4 a few days ago and haven't found how to solve it yet. Did some rework on MP4 6x chassis and remake some parts
All the reworks up to UV mapping and UVs sets was done using Maya then exported as *FBX and imported into Blender 2.93
At first when just imported the models looks ok, but how long I apply a SCS' Material the issues appears

#1 - Most common is this black shading covering most of the new parts, tried edge spliting, create new UVs on Blenders, flat/smooth meshes but the problem persists
this image theres the new fenders for Actros and the original DAF 2021 rear fenders as reference
[ external image ]
[ external image ]

#2 - Tried apply the same material as DAF 21 plastic fenders on the new fenders for MP4, UV_0 and UV_1 mapped as such, it looks ok at first but it gets broken after while be when changing something related to textures or after exporting into game, it gets broken anyway, on this image below the top fenders uses the same material as vanilla MP4 plastic fenders (carpaint_color, normals etc) apparely the only issue is with black part (#1) and bottom fender I tried the same as DAF 2021 but looks as the mapping is completely distorted
[ external image ]

#3 - Similar to #2 tried apply same material as DAF'21 fuel tank (alu_base texture) on the new MP4 tanks but as it just gets the same problem like #2 so I tried to use the vanilla MP4 material (metal parts) but the model presents these hard edges like if the model was was splitted in 4 pieces - but only when material is applied
Maybe i'm missing a very obvious solution but I've been looking for a few days and without success
[ external image ]

I have very little experience with Blender, use it only for ETS exporting, parts I did just minor reworks as chassis main frame and rear bumpers looks ok ingame, but the ones i did major rework like fender presents these issues on materials

[SanJose [PL]]

Check the vertex color in Blender on those parts. Diffuse color in material properties will be also the clue.

[Ma7heus]

Yes Thank You @SanJose [PL] really the lack of edits on Vertex Paint mode was the cause of the black shading issue. looking around for some guides about vertex colors I could learn a bit how it works, was getting tired of all this what made me create this topic out of frustration but now i got a much better result in game

As for the weird shading on fuel tank model it was because I was trying to apply an edited normal map textures (tga) on it, so whenever I applied it the objects using this new normal map were getting weird
The other issue about distorted mapping was when I tried to use custom materials then the objects that used it looked like the uv mapping was broken
the temporary solution for both was to use the exact same material and texures as the DAF 21 parts I had as a reference, so this Actros now uses some textures like normals and decals from the DAF 2021' folders
Not a big deal for me as long it works in game but I'll look around to find out how to use my own materials without getting these issues again. Thanks!

[ external image ]
[ external image ]

[SanJose [PL]]

To get the best results you should also re-do or create completely new uv mapping for fenders and adapt it to the textures from Daf.

But in my personal opinion better is to create new texture but keeping the old UV mapping as a reference