it just ocurred to me that if the contacts on the relay bent too much, you might contact your 120v line with your computer's 12v line, and that'd fry everything in the case for sure... I though of it because a joystick microswitch in my cab was having issues, and I looked under and found that when I'd plugged something in, it had pulled a cable that was hooked around another cable, and bent a contact and shorted the switch. Guess you can't be too careful.
So, use insulated quick disconnects, or give it a healthy dose of hot glue over the whole contact side of the relay, or use a relay socket, or something, if you hook a relay up to 120v.