The Power Drain Computer is required for creating functioning Power Drain systems. It is capable of controlling any amount of Power Drain Modules, although using multiple groups leads to escalating power costs. Once placed, you can select/deselect it with C, and link Power Drain Modules using V while it is selected and you are looking at a Power Drain Module. This controller can be connected to other weapons and systems (cannon, beam, pulse, missile) to customize your weapon

First the controller and then the module, so the module is connected to the controller. You can then select another weapon controller with C and then press V to hook this weapon up to the other weapon

Note, that for the full effect, you need to connect 1:1 in size
Press (R Default) to get in/out of the Computer.