How do you "Activate" pre-existing mounting points for accessories?

[Wrecked911]

I made bullbars for the 2019 Freightliner Cascadia and I see it already has a mounting point for bullbars on the chassis file, but I can't figure out how to "activate" it for in game.
I've been following Half Fast Gaming's tutorials from 2022, and while a lot of the stuff in there is great info, some of it is outdated, and this one especially has me stumped.

What assets/files do I need to change?

PS, I'm also following the sun visor tutorial, and made an edited copy of Chrome Sun Visor Sharp where it's comically pointy. It shows up in the mod list and the truck accessories list... but the exterior model falls back to the original model, and the interior model is invisible/doesn't exist at all. Does anyone have any newer tutorials to use? I absolutely have to be missing files, or something.

[Wrecked911]

After several days of throwing stuff at the wall to try to get the unused hookups on the Cascadia to work, I've given up and have just started piggybacking off of existing hookups.
Bullbar? Add it to a Bumper.
Roof Lights? Add it to a Sun Visor
Marker lights? Add it to a Sideskirt.

It's dirty, as I hate muddying up the accessories list with improperly organized assets, but I've lost enough time trying to crack this. With some luck and more experience I'll probably figure it out eventually, but until that day comes I'm just gonna have to work around this limit.