Go north and exchange the toolkit for a fuel cell controller. You'll need that for the car, so hang on to it. He'll also tell you he needs something else from one of the ghouls in the reactor.
Go in the reactor building. You'll have to reach Festus, a ghoul in
the far east room. Unfortunately, you have to pass through a door
which needs a yellow keycard, and noone gave me the card, even though
they had asked me to repair their reactor. The one from the crashed
vertibird didn't work, and lockpicking the door causes the guards to
attack you. So I just stole the keycard from one of the guards in
front of the door. (And I also stole both guards' ammo, while I was
at it :)
Later I found that there was a yellow key in a locker elsewhere on the
floor, so you may want to look for that if your steal skill sucks.
Also in a cupboard this area is a blue keycard which, although I think
it's useless here, fits a door in the Navarro base later. There is a
similar blue key in the Navarro base, too, so it's not strictly
necessary to carry this one along, but if you have this one from
Gecko, you can take the back door into Navarro.
The only problem here is that Festus is scared silly of repairing the
reactor, for some reason. With good speech skill, I could convince
him. Without, I had to install it myself. To install it yourself,
you can try to program the repair bot. Me, I just told Sulik and Vic
to stay there, took the one RadX I had, and made a run through the
reactor room, then used the repair skill on the thingie next to the
valve on the eastern wall. I took a lot of damage and got radiated in
the process. Too bad I didn't have 2 RadX's, but one Rad-Away took
care of that. (And got me addicted to Rad-Away... WTH??)
Now for the transformer the ghoul up north wants, you can steal a
requisition form from Festus, then go with it at the ghoul with the
supply cabinet. Or you can steal the transformer directly from the
ghoul with the supply cabinet, since in the game there is no actual
supply cabinet, and he has all the items on him.
Talk to Festus again, and he'll give you a disc with the reactor data
that you can use on the Vault City central computer to optimize the
reactor. Leave this building for now.
Go to the ghoul north, and give him the transformer. He'll offer to
modify a weapon for you for free. Neat, huh? Installing the night
sight on a FN FAL was my favourite, since then I could use it at night
to snipe the slavers back at the Den, while they had massive penalties
aiming at me in the dark. On the bad side, it doesn't have JHP ammo,
and generally the single shot damage is a bit disappointing, while the
burst mode uses too much ammo. But normally it's the most expensive
weapon upgrade, so I figured I'd better make the most out of that
offer to do it for free.
Leave back for Vault City...