LMM no crank no start or gear indicator lights up.

Well I have a 07 lmm 3500hd. It wont crank or start. Also the gear indicator doesn't light up. So I bought this truck wrecked sight unseen 2 years ago. Never do that again. Anyway turns out it needed a frame. Which I bought. Didn't get around to swapping frame until last September. I drove it into my shop and it always started. Even with crap batteries. So I disassembled the truck during the winter. Fast forward to April trucks back together enough to try and start it. Unfortunately no luck. I've tested just about everything , but I'm still missing something. Tried a different ECM,TCM no start. I only get 9.87 volts on the starter relay. Pin 86 I believe. Pin 30 I get 12 volts. The truck will start with a push button connected to the starter if I unhook the TCM and put jumper wires on the Can Bus network. That's the only time my scanner will talk to the truck as well. Sorry for the long post. The thing is driving me crazy. Any ideas would be grateful.

(Just a shot in the dark...) Are you missing a ground wire? Make sure you've got heavy connections between battery negatives, engine, frame and body.

Oh, lots of the time critical grounds from things like ECUs and sensors will all ground to one point, maybe on the engine. Bottom line, make sure they're all present and connected where they're supposed to be.

I did have one break off. It was from the oil level switch, but since I painted the frame maybe I should clean those spots down to bare metal just in case.

If the ONLY indication is no shift range indicator and no crank/start, focus on the NSBU, and/or its conductors/connectors. If it's failed or not properly connected (and grounded), it will do exactly that. The NSBU does 2 primary things: controls the range indicator; inhibits crank/start if not positively in P or N.

I just haven't figured out how to test the NSBU since its inside the tranny. The main connecter to the tranny has been leaking a bit also. I cleaned it and put dielectric grease in the plug. Is there a way to fool the switch to make it think its in park? What bugs me is I drove it into the shop last fall.