Par,
As ewh quite rightly points out it's logical to model the Part / Assembly in it's vehicle line position so as to check mating issues.
Within C3P Ideas, the option is available to model the component either in vehicle line position or at global.
The question come's as to how other users...
One of the "big three" uses the following dimensions when
locating the Vehicle Origin from where all vehicle dimensions are taken from.
The X plane runs from front to back of vehicle when viewed in side view ( front of vehicle pointing left).
The Y plane runs from side to side of vehicle (...