You will unlock Undead Man’s Party Bus achievement in Black Ops 2 when you completely upgrade your bus with all three possible additions in the Tranzit campaign. Let’s get straight down to business and find out all the upgrade parts in Tranzit Zombies mode.
Basically, to get this achievement you need to get three upgrade parts, which are hidden throughout the Tranzit maps. These three upgrade parts are: the grill, the roof hatch and the ladder. These items randomly spawn on four locations. These locations are:
Note. Before you upgrade the bus, you need to build a turbine. For that you need to grab a mannequin from the central map, a wing of a toy plane from the nearby payphones and finally, a fan which is right behind the workbench. Place them all one by one on the workbench and you have created a turbine.
Bus Upgrade #1 Location. Place the turbine you have created right next to the door to the right of the workbench. When the door is opened to the room, it will have inside the grill. You can attach this grill to the front of your bus. By doing this you will not allow the zombies to enter through the front window of your bus. Remember to keep the turbine with you.
Bus Upgrade #2 Location. After adding the first upgrade part, go all the way to the shed near the diner. Use the fan to get in. At this spot is the roof hatch. Take it back to the bus and get it into the bus. Go to the middle of the bus, look up and jump so you can attach the hatch to the roof. With this roof hatch attached, you can now jump up anytime from the bus to the rooftop.
Bus Upgrade #3 Location. After retrieving the second upgrade part, go to the Farm and head towards the back of the farm to another shed. Use the turbine to get in there. The third and final piece; the ladder is in here. Go back to the bus and attach it to the back of your bus.
Location For Missing Upgrade Part Location. If one of these parts failed to show up on any of these locations, there is a 4th place you can check. The 4th spot is at the terminal. Go in through the bank vault area. Make a left and then right, follow the pavement to another locked door. Use the turbine to open that door and inside would be the final part if you do not have it already.
Once all three parts are attached to the bus you will unlock the “Undead Man’s Party Bus” achievement.