1992 Jetta problems

Just replaced heater core on 1992 Jetta, radio and blower fan have no power and when I turn the key to start it just clicks. There are three connecters in the back of the radio but i only have two. I think there should be three if that helps any.

Radio usually only uses two of the three connectors. If the items were working when you started something was left loose. Otherwise check connections at ignition switch.