The Ambulance can be found near the sewers entrance in the Value Voltage area. It can be activated by hitting the switch on the left side of the vehicle for 500 points. When activated, it will trigger the ambulance's siren, that will attract zombies in the area. It will last for 15 seconds before a 60 seconds cooldown occurs, during which the player cannot use the Ambulance.
The Ambulance is very useful if one does not wish to use their Camouflage or Distraction Drone. If the player has to escort a Survivor to the Value Voltage area, the Ambulance is a good utility to use to distract the zombies away from the survivor until he is extracted. It is also helpful if one needs to revive a downed teammate.