get someone to help you and while they crank it you check voltage
1. at battery
2. at the main wire at starter
3. at the solnoid on the firewall ( assume this is a ford solnoid?)
also is it just clicking because its hung up on the flexplate ?
If all the voltages are about 10 at the places above while cranking, its a ground issue. Take a ground from the block to the frame, what size ground on the battery and where does it go to ?