1995 Ford Mustang loose all electrical power when key is tu

I have a 1995 ford mustang v6 3.8 liter automatic,

situation- pulled up to a store and got something to drink. Went back to the car turn the key over and heard a click and lost all electrical power, the starter never had a chance to engage. Now there is no power in the car anywhere.

troubleshooting- pulled the battery terminal off and put back on and all electrical is restored but as soon as the ignition goes from run to start I loose all electrical again, I have repeated this process over and over again. The only thing that I hear is a low click right before power is cut off. I replaced the battery and the symtoms remain the same. Please help me figure this out