For what it’s worth, you can easily determine which side of the starting circuit is the issue.
- If you have an auto trans make sure the car is in park.
- If you have a manual trans make sure the car is in neutral, and e-brake is engaged.
Look in the engine compartment relay box and find the starter relay. Pull the relay and look for the diagram on the side of the relay. When you identify the (usually two) pins that switch the circuit (not the control side of the relay) use a paperclip and momentarily jump them at the fuse/relay box under the hood to start the car (make sure your key is inserted and turned to the ‘on’ position before doing a relay bypass).
If it starts: than you know the battery, terminals, cables, trigger wire, ground, starter, key (if it has a chip) and ignition switch are OK.
I should have done this first recently, and didn’t; I wasted time and money on a 2005 Mustang V6 (manual trans) no start/turn-over condition. After performing the aforementioned troubleshooting, I was easily able to determine that it was the clutch safety switch that had failed; if you have an automatic, check the park/neutral safety switch for a failure.
Lastly, after determining the issue with the CSS - it was easily bypassed by shunting the CSS circuit with another paperclip after pulling the plug (till the new switch comes in).
Returned the starter, and saved big. Win. GL!