I ran out of tank ammo. Where can I replenish it?
Drive next to a Sunderer infantry transporter (see below) or ammo supply tower to replenish your ammo. This will also repair any damage on your vehicle.
An ammo supply tower. Watch out for the holo-icon on the top. These are easy to miss since the HUD icon blends in nicely with the top, which makes them look like regular, non-usable world objects. The HUD icon is also slightly misleading - if you don't have a direct line of sight you may think this is an aircraft supply station.
Note that not all Sunderers can resupply your ammo: only ones with "Vehicle ammo dispenser" in their loadout. A Sunderer with this feature equipped has the same holo-icon as the ammo tower on its sides, and on its minimap icon. The Sunderer doesn't need to be deployed or even stationary to resupply you.