Check your battery. Usually when you get the clicking sound that means the battery is dead or in need of charge.
If the starter is engaging and the starter is able to turn the engine normally, there is nothing wrong with the solenoid. Instead, I'd look at fuel, ignition and compression.
Dead battery? Loose or corroded battery cables? Seized engine? Defective starter solenoid? Defective starter? Defective neutral safety switch?
Seized engine? Bad neutral safety switch? Bad starter or starter solenoid? Loose cable connection at battery or starter?
A solenoid is a type of magnetic switch responsible for helping your starter motor turn on the engine. When the solenoid sticks, the ignition struggles to start. When this happens, usually your key will "catch" in when you turn it to start the vehicle.
On the 4.6L engine. The starter solenoid is located on the passenger's side firewall. Next to the hood hinge. Just under the plastic hard shell cover. It's a black cover on the firewall. Pull cover off and you will see the solenoid relay switch.
The solenoid on a Caterpillar C15 diesel engine can be found on top of the alternator. The solenoid is held on by four screws.
The camshaft actuator solenoid is located on the back of the engine. The solenoid will be near the top of the engine just below the cylinder head.
The 2009 Ford Expedition has a V8 engine.
The 2012 Ford Expedition has a V8 engine.
The 2010 Ford Expedition has a V8 engine.
The 2014 Ford Expedition has a V8 engine.
The 2013 Ford Expedition has a V8 engine.