Gas to Diesel Conversion on 95 Chevy Cheyenne

About 5 years ago my dad did a diesel conversion on (what is now my truck), a 95 Chevy Cheyenne from a gas to a 6.7L Turbo Diesel. Not that it's under my name I'm trying to fix it before summer but the truck wont start. My dad said that when he turns the ignition it wants to start and you can here cranking but it just wont turn on.

We discussed that when we did the conversion he left the Allison tranny. So we're thinking that the wiring harness for the new motor isnt compatible with the transmission. So could it be that the tranny doesnt read that the truck is in parking so it wont let it start or could it be something in the wires? Please help I would really like to get this truck up and running. thank you

 

6.7? Check the usual things such as fuel flow, compression, timing (as much as you can), grounds, battery charge, etc. Try hitting it with a dab of ether. Did the engine come with an Allison trans? Because I am not aware of any Chevy 1500, 2500, or 3500 that came with an Allison at that time. Are you sure its not a 4L60 or 4L80 or 700R4? There are stand alone trans controllers for some trans, so research that.