Remember this is a 2011 Fiesta, and with an OEM original Wiring harness - and if you had issues with the system before this starter issue, - the problems you have now might not get resolved unless a continuity check is done on the wiring harness - including the harness UNDER the battery tray.
So, if you have had a leaky battery or older damaged battery in the tray - it can leave a trail of battery acid that leaked into that harness - doing a lot of damage in the process.
This may be a simple open wire - but a continuity check has to be performed to verify the wiring makes contact at all the points it routes and connects to.
To help, that Starter inhibit relay is the one that engages the SOLENOID of the starter.
You say you verified the starter does work, but does the plunger engage? That is the job of the Solenoid - it has a plunger that works as a piston to press the spring down and engage the starter gear that rotates off the shaft of the starter. That gear gets pressed onto the flywheel's teeth.
So, you're not getting a CRANK signal? Yet, you did have one earlier - now you're thinking it's the IGN switch.
Ok, So you're not seeing a display of the messages I asked you about earlier, it is my fear that when you worked on the Clutch and transmission there may have been a wire to the solenoid - or on the starter itself, that got damaged or pinched in the housing and now the fuse is blown, or the wire when it got pinched, shorted out and blew internally like a fusible link and that wire will have to be replaced or somehow that pinch point and the blown portion - will have to be patched with new wire.
To help find that - is a lot like a needle in a haystack - sometimes, you can find it right away, other times - you'll take a long time in what seems like a fruitless, pointless search.
Well, to help, look at it from the standpoint of what is getting power from where - you know you have KEY for you have Ignition...
But, does the Dash light up all those ICONs in the START position?
IF not, then look at post 7's graphics - see that Blue wire? Heads off to the PODS on the Dash, that means the IGN and START are forcing those ICON (Idiot Lights) on - by putting power into that wire.
So, if IGN shows the LIGHTS, great, but does START do this too?
Then the White-Green wire by default, would also force a display message (Audio Control Module ACM) - your - PRESS CLUTCH or PRESS CLUTCH AND BRAKE - to START.
White Green wire heads to power the Relay in the Engine compartment from START. (Hot only in Start)
So the above might help provide your mechanic a route to take to trace and track down those wiring issues.
If you don't get these colors on your TV set...
If no lights to the Dash, that Blue-white wire is damaged or open or not seated.
The Yellow wire grounds at the PCM - forced when the PCM sees NEUTRAL or PARK or CLUTCH switch - being engaged - clearing the Wait condition until you do this - in the message display.
So locate the big Junction Box in the engine compartment and look for that starter relay - and trace that set of contacts to do a continuity check to the PCM, battery and the IGNITION switch and its harness to see if the wire is still good.
