Switching weapons on a vehicle?

I have two different weapons mounted on my plane, one on mount0, and one on mount1. Both show up correctly, but when I hit the trigger, only the one on mount0 fires. I tried looking through the source code, but I couldn't find a function for switching weapons on a vehicle. Where should I start looking?

(PS: This vehicle will NOT be mounted by a player, so i think putting my weapon on mount0 should be ok...)

thanks!