My '99 F-150 wont start I replaced the starter, solenoid, battery terminals, and my battery is one year old I checked the voltage on battery it reads 12.5v I still hear a click coming from the starter and thud coming from the fuse box what can it be, I switched relays and still wont start

First turn the engine over by hand. You usually can do this by grabbing the belt and pulling on it or by putting a socket and ratchet on the front of the crankshaft. Make sure the crankshaft turns. If the engine does not turn then your engine is seized (not good) If the engine turns check the battery voltage at the battery while you are trying to crank it. It should be no less then 9 volts. If that checks out do the same but hook the positive lead of your meter to the big positive starter wire at the starter. The voltage should be very close to the voltage from the first test. If that fails your looking at the start cable or relay. You can do the same test on either side of the relay to figure out where your problem is. Next you can check for voltage drop on the ground cable. Hook one end of your voltage tester to the negative battery terminal. Next hook up the other end to the other end of the negative cable or the engine block. Try to crank the engine while watching the voltage reading. It should not read more than 1 volt. If it does replace the ground cable. If everything checks out then you have another bad starter First turn the engine over by hand. You usually can do this by grabbing the belt and pulling on it or by putting a socket and ratchet on the front of the crankshaft. Make sure the crankshaft turns. If the engine does not turn then your engine is seized (not good) If the engine turns check the battery voltage at the battery while you are trying to crank it. It should be no less then 9 volts. If that checks out do the same but hook the positive lead of your meter to the big positive starter wire at the starter. The voltage should be very close to the voltage from the first test. If that fails your looking at the start cable or relay. You can do the same test on either side of the relay to figure out where your problem is. Next you can check for voltage drop on the ground cable. Hook one end of your voltage tester to the negative battery terminal. Next hook up the other end to the other end of the negative cable or the engine block. Try to crank the engine while watching the voltage reading. It should not read more than 1 volt. If it does replace the ground cable. If everything checks out then you have another bad starter