@Bmhdg76 umm where do i find the towbar compliance plate?
Ummm... Maybe try the tow bar.
If it's an after market fitment it should be on there, if factory fitted go back to the dealer if you can't find anything or check the vehicles manual.
Also keep in mind some manufacturers reduce your vehicles cargo capacity (thus GVM) for the more down load you put on the tow ball... This will be in the manual too if applicable.
This might help explain a few basic...
http://www.racq.com.au/motoring/driving/towing/trailer__and__tow_vehicle_specifications_explained