@tr2rf First of all this mod works with 0.30.x game version, I don't know if it works to the older version (in that case you can try the old version of semi_trailer.zip around the web). This mod could be collide with other trucks mod, so you must try to launch this mod without other track mods (and when it works, try to re-insert one by one your trucks mods).You also need to remove old version of semi_trailer.zip that could be stored inside the  mods/repo folder. Try to clear the cache to the standard mode. If you compare the sizes of this version to the older you can find this version is 100MB, old version 40MB, this is because I've re-inserted all textures and their correct paths.

@Bolt2407(Totally_not)_Beamfan The "Trailers in Parts Selector 1.02" you mentioned is experimental, broken and non-working mod. You can check what I said on the official beamng website.

@eredegames the other mod i mentioned LITERALLY does the same but also offers the other trailers for other vehicles.

@Bolt2407(Totally_not)_Beamfan This mod need a fix because was broken in trailers textures and doesn't add pipes on trails, this because the file materials contained incorrect paths. The purpose of this mod is to have trailers already attached on spawn.

@ayzenxl You must remove the old version and clean the cache. The old version could be stored on mods/repo folder. Let me know, I will help you.

@mrhevor The textures on the vehicle become orange