Wow you was no help to this guy^
Basically all you gotta do to install a vehicle mod is go to, in OpenIV, your mods folder if you have one, and then go to update, update.rpf, common, data, dlclist.xml
Scroll down to the bottom and select one of the indivdual path lines. It looks like this
<Item>dlcpacks:/mpchristmas2018/</Item>
<Item>dlcpacks:/patchday21ng/</Item>
<Item>dlcpacks:/mpvinewood/</Item>
And add paste a new line with the path being the name of the addon folder. For example:
<Item>dlcpacks:/mpchristmas2018/</Item>
<Item>dlcpacks:/I like big butts and I can not lie/</Item>
<Item>dlcpacks:/mpvinewood/</Item>
Then save that file. Then navigate back to mods/update/ and this time open x64 then dlcpacks, inside there, drop the addon folder. Job done!
Let us know how it goes! Best care model to ever be made for this game is the MWB124 by @SparK_v
Check out my driving script