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There is only one starter solenoid, on the starter motor, but it is popular, if not accurate, to call the starter relay, on the inner fender, a starter solenoid.
On the fender is the starter relay, it will have 2 large posts and one smaller post, small post will have an "S" Label.
The "S" wire on Ford's is almost always Red/light blue stripe wire.
This is the wire that comes from the Key switch, and passes thru the clutch switch.
It will have 12volts when clutch pedal is in and key is turn to START.
That 12volts activates(closes) the Starter Relay.
On one of the larger posts of starter relay will be the Battery "+" cable and with it several other cables and wires, this is the Power distribution point for the electrical system.
One the other large post will be 1 cable only, it will run to the large post on the starter motor.
When "S" wire gets 12volts Relay closes and sends full battery voltage to the starter motor, and starter solenoid, solenoid pushes starter gear out to make contact with flywheel and engine turns over.
One big piece that is missing in this, battery "+" voltage is useless without battery "-" voltage, the Ground.
Battery "-" should have a cable running to the engine block, often to one of the starter motor bolts, but to the engine for sure.
Starter motor and alternator are the biggest AMP users, and both are on the engine.
So first thing to do is remove the key from the vehicle.
Put transmission in NEUTRAL..............!!!!!!
Park Brake ON
Get a short wire
Put one end of the wire on battery "+" and touch the other end to the "S" post on starter relay.
Relay should click and starter motor should turn engine.
If relay clicks but not starter movement then not enough AMPs are going to the starter motor, simple as that.
Could be loose battery cables, either end, REMEMBER the Ground!
Bad starter relay
Bad cable from Battery to relay, bad cable from Relay to Starter
Now just a heads UP:
My 1994 4.0l doesn't have a starter relay, it has what "looks like" a starter relay on the fender.
But my year was the first year of putting the starter relay ON the starter motor.
So the starter motor has the smaller "S" post and the Red/Light Blue wire is there.
Basically they combined the solenoid and relay into one unit since it was easier.
If you look here: http://www.ebay.com/itm/New-Starter-...BWKQpP&vxp=mtr
You can see the smaller "S" post for the Red/blue wire.
On these the battery "+" cable can run directly to the starter motor's large post(top one in picture), or it shares the same large post on "starter relay" as the battery "+" cable so starter motor is always connected to battery "+".
The "S" wire activates it
And just my pet peeve
A solenoid causes mechanical movement
A relay connects and disconnects an electrical circuit
You might use a solenoid to open and close a valve for water or ??
And you might use a relay to control that solenoid, lol
Similar to starter motor setup