Having trouble with my 2003 f250 5.4l. I turn the key on the truck and makes a clicking sound just once or twice and truck won’t start. I replaced the battery terminal connectors a new battery and a new starter. Still didn’t fix it. Any advice helps. Thanks

 

If you can, have someone try to turn the key to the start position and see if you can feel/hear the starter relay in the engine compartment fuse /relay panel work.

Depending on what result you get there will determine where we go next.
By the way, make sure you check ALL the fuses there.
Is your truck stick shift or automatic ?
We just had a similar situation with a Ford Taurus. Procedure is the same.

 

Engine off key out, then locate C2163 (starter relay) above and unplug the relay.
Once unplugged carefully identify and remember the pin orientation as shown below:

1) voltmeter red to battery + post, black to - post what voltage you get?
Put the relay at somewhere else you don't need that for now.
2) voltmeter red to pin 30 (female side) of starter relay socket, black to - post of battery, what voltage you get, same exact voltage as (1) or a bit lower or no voltage? If no voltage check F2.113 (30A).
3) ohmmeter red to pin 85 (female side) of starter relay socket, black to - post of battery, resistance less than 5 ohm or not? Also make sure it's always ground and no switched ground, so check continuity on this pin 85 to battery - post to make sure it beeps.
4) voltmeter red to pin 86 (female side) of starter relay socket, black to - post of battery, turn key to START position what voltage you get? If 9.6V or above it's good, if it's 0V check F2.31 (15A) fuse first using ohmmeter or check for continuity. Whenever you have a multimeter always inspect the fuse that way, don't just inspect by looking at it. If it's 0V but the F2.31 (15A) is good, you can stop here and skip 5-6 below, the issue is from ignition thru range sensor up to terminal 86.

If the always hot power feed of circuit 2037 (RD) to pin 30 is good, always ground of circuit 57 (BK) to pin 85 is also good (less than 5 ohm) and you get 9.6V or above on circuit 1093 (TN/RD) to pin 86 then:
5) unplug the relay still, turn key to ON position, run a jumper wire (8 to 16 gauge if possible) from pin 87 to battery + post:
if it cranks then the relay is not energizing you need to bench test the relay or find an identical relay to test. It can simply be a bad relay or its wiring.
If it doesn't crank you need to check the starter solenoid (it's attached to your starter motor), voltmeter red to S terminal of the starter solenoid, black to - post of battery or a good ground source, key out (not needed), but same jumper wire from pin 87 to battery + post. This is to check if your starter solenoid is getting 12v feed from battery + post thru terminal 87 to the S terminal or not. This also tells whether or not you need to bench test your starter motor.
6) unplug the relay still, key out and remove the jumper wire from (5) above, ohmmeter red to pin 87 (female side) of starter relay socket, black to S terminal of starter solenoid, resistance less than 5 ohm or not?

S terminal check above diagram circuit 113 (yellow/light blue)

If you want you can also go thru the pinpoint test as shown below but that can be a bit more challenging:

 

I replaced the starter the battery the 30 amp fuse the relay the battery terminal connectors and a new battery and still doing the same thing. I can feel the relay clicking when I try to start the truck. But when I turn the key it just clicks once.

 

It is supposed to click once if you turn it to start once, but the message signal from the start relay may not be getting to the solenoid on the starter.

 

There is a junction block in the engine compartment that is located on the driver's side fender well that gets exposed to all kinds of weather and,it does become corroded.

Make sure to loosen the nut, clean the connections and reinstall the nut and lock washer. Just be careful working there because that junction is supplied power directly from the battery positive terminal.
Touching any metal on the truck and that connection at the same time can create a short circuit and a lot of sparks and heat.
The smart thing to do would be to remove the negative battery cable before cleaning the junction block connections., then when finished reconnect the negative battery cable.