Click,Click,Click!

Need some help. Went out to my Dart and when I turned the key to start all that happened was a click from the starter and then nothing. Dome light went out, and when I tried to start again, nothing happened, not even a click. Thought battery was low so I hooked up the charger.
Next day I tried to start engine again. Same thing happened as day before. Pulled battery and took to parts house and battery checked out good. Put battery in and tried to start again. There was a click from starter and then nothing.
Checked battery with voltmeter and is reading 12.49. At the starter relay reading is 12.49. Tried to jump across post on start relay. Click from starter then nothing. When I try to jump across relay again, nothing, no click at all.
Tried giving starter a tap with rubber mallet but no luck. Thinking that maybe the starter relay is bad or perhaps the starter. Would like some ideas as to what to do now.