I have a 2005 Sport Trac Adrenaline with a NO Crank issue. It cranked 2 days ago but today doesn't. I didn't touch anything. Just installed a fuel rail sensor and now won't crank. Also won't start when it did crank. The Fuse box doesn't look like any other I've been able to find.

I've checked All fuses & Relays and battery is new and charged

Starter is new and getting power when switched on.

 

Don't forget if we get a normal power reading from the positive side of the system when we check it, the other half of the electrical system is the ground side.
There, as you know, you have 2 choices to check . One is to remove clean and reinstall all connections coming from the negative battery post to wherever they connect top the vehicle. The other is to do voltage drop tests to verify the connections are not offering resistance that prevents full electrical flow.

I have seen many times where the cable connection to the battery post looks fine, but if there is oxidation at the lead post OR cable end, which by the way looks just fine, but IS NOT !
A simple step that can make the difference, just clean them with a wire brush, sandpaper or battery terminal cleaning tool. (Always a good investment)
These are some of the simple , but important things to remember.