If you intend to get anywhere in Tranzit, you’re going to need the Pack-A-Punch machine. This device will power-up your weapons to help you survive the zombie hordes. To build the Pack-a-Punch you need to gather three items from the Bank in the Town; the Table, the Battery and a Head Piece.
In the power station there is a door with a lightning symbol on it, you need to put a turbine near here. Next go to the bank and into the vault (open the vault doors with grenades). Eventually you will find another door with a lightning symbol which should be open if your turbine has not been destroyed yet.
Proceed into the room and collect the three items, construct on the nearby workbench and use it to upgrade your weapons to your hearts content. For more help on Black Ops 2 Tranzit, read our Buildable Items Parts Locations Guide.