1980 FB RX7 no crank
 

My fb wont crank. It has new battery, plugs, alternator(tested good), starter(tested good), and new main power and ground lines. When i turn the key every comes on but as soon as i try to crank it clicks and losses al power to wont come back. I checked with a multimeter and i do 12v to everything but im now at a loss and dont know what could be wrong. The motor is not seized.

Have you done a voltage drop test on the main power lead for the starter? Could be making enough of a connecting to push 12v, but as soon as you try to jam 150 amps down there it could break the connection

The first thing to check here is to make sure the battery cables are tight on the battery posts. Where in Ohio are you located?