Too long since I've played it. But this might help: http://gamebanshee.com/fallout2/locations/gecko.php

Thaks, but none of the walkthroughs for this game deal with interface issues. I'm looking for help on which button to click where, with respect to using the red passcard. I know I have to use it, and I know which door I have to use it on The problem is HOW to use it on the door.
The obvious -- the usual game interface technique -- doesn't seem to work here. For instance, when you use a key to open a door in Trapper Town, you put the key in one of the two inventory slots, go out of inventory, then "use" the key on the door. That's what I've been doing here, and it isn't working. So I'm left wondering what to do to get past this locked door in the Reactor building in Gecko.

Are you absolutely sure it's the right passcard? Sure it's maybe not supposed to be unlocked via a terminal/computer?

I had the same problem when I played through Fallout 2 recently. Are you sure you are using the red passcard on the red door, not the yellow one for example? :) If you are sure just try to "use" the door once you've used the passcard on it and if it doesn't work, repeat. I'm not sure what my problem was or how I solved it, but I think it just didn't tell me "You've unlocked the door" like it usually would, although I did unlock it.

I just did this recently. I put the red passcard in my quick-item slot (where weapons normally go). Then click it THERE, then the door. Hope that helps.

This should work... normally though what I do is right click hold on the door, go down to the inventory icon, and choose the correct security card. That should work, if its not, then a) there's a bug or b) you're using the wrong card or c) I'm retarded and don't remember anything correctly (but I'm fairly certain)