LMM: Turn the key...engine won't crank

[ToddO64]

On my earlier post, I stated that by running current directly to the starter it will crank but not start with ignition with vehicle's batteries. What should I do next or suspect fuse link where do I look?

Keep in mind this is for a 2010 Express 3500 with a 6.6L Duramax Diesel.

 

[ToddO64]

I have a 2010 Chevy Express 3500 with a 6.6 liter Duramax diesel. With the key on dashboard lights up. With the key to crank position, it has no crank. Direct current to starter solenoid allows crank burnout start. I checked obvious fusible links and fuses. Replaced under hood power distribution center and ECU. Where should I suspect to test next? I am stumped.