03 7.3 wont start after setting for 2 or 3 days checked all glow plugs all good checked timer, glow plug wiring good could it be a injector bad or what.i have to keep it plugged in @ all times and inside where its warm and start it every day or crank and crank on it til it starts if left outside or not plugged in.

 

Check again... Its a glow plug issue if it will not start when cold but starts fine when warm

Put a test light on the glow plug relay and watch it. when you turn the key on it should light and stay on for about a minute or more.

 

had one do that in our shop. test lights are great but might try a meter to make sure you have the full 12v