When you enter Gecko, go to the nuclear plant and talk to Festus; convince him to install the Hy-Mag. If your efforts are fruitless, save the game in a different slot, and enter the nuclear reactor. Go to the red coolant valve and use the Hy-Mag there. It'll take a few tries to get it to work. You'll lose a lot of hit points because of the intense radiation there. If you've got a high enough science skill, you can use the computer terminal to fix the reactor. This is what you do:
Then choose 'add a command' again and add the following:
Then you end the program and then execute.
After it is successfully installed, save the game. Also, talk to Festus again, and get the optimization data for Gecko's power plant. You can also go and talk to the ghoul who handles the storage and barter some ammo for another 3-step Plasma Transformer. Also, go to the north end and talk to Skeeter. Give the tool kit to him for the fuel cell controller. Save the game and successfully steal the tool kit. Give Skeeter the plasma transformer, and he can upgrade another one of your weapons. Save, and head for Vault City.
If you've looked closely, there's a working computer in the reactor control room. You can chat with an Enclave guard (talking head and all) - it's a very humorous conversation. Here are the steps you'll need to take: