It's always a good idea to disconnect the battery when working with anything electrical, that being said I didn't but I like to live dangerously. The circuit board is removable, you need to take all 4 screws out and disconnect the gray plug going to it and it'll be free. I certainly wouldn't want to solder it in the car, I don't like to live that dangerously It would be nice to have a fine tipped soldering iron, but I just used a normal one and it worked OK. I'm no pro at soldering either so I wouldn't worry too much about it, just keep the solder off the board to the best of your abilities and it'll work fine.