This probably ought to be moved to the rules section, but
AP does have an effect on the vehicle damage chart, but not on the penetration rule.
So you roll your
D6 and add the strength of the weapon (plus any other modifiers for weapon type such as melta etc) and compare to the vehicle
AV.
Then you roll on the vehicle damage chart, and this is where weapon
AP has an effect.
I'm afraid i don't have the page numbers but sure somebody will be able to provide them.