The 2003 3500 HD we have had a 6.0 that let a rod loose and went thru the side of the block.
Since this truck is only used on the farm in a limited role we opted to buy a really low mileage 5.3 that was
complete (less than 5k miles) for 450.00 and put in it.

We have completed the swap, everything plugged up identical, no differences in wiring harness. The motors
even call for the same # ecu.

Now that we have it in and everything hooks up it is dead, won't crank. When hooked to a scanner it shows
no communication with the engine and tranny. It will read the dash, air bags, etc, but not the engine or
tranny.

The dashlights sometimes want to stay on with the key pulled out.

We know that the ecu is good, even tried putting a new one in, but have the same results.

Any ideas on what the issue could be? Any help would be appreciated.