2006 Sierra 2500HD 6.0L No Crank

[JohnDeereJoe]

Hey everyone, I'm running out of ideas trying to find the source of this no crank condition. So this past weekend I replaced knock sensors, oil pressure sensor, engine ground strap, MAF and did some welding on the exhaust. It started up after welding. When going to start the truck, everything in the cab lights up. Dash, radio, interior lights, cab lights ect. Nothing happens when the key is turned to crank it. When the key is pulled out of the ignition, everything still has power and will not shut off. There is no communication with the OBD port so I can't hook a scanner to the vehicle. I've checked all of the under hood fuses and everything has power. Fuel pump is not priming also with the key on. I pulled the starter relay and hooked a jumper wire up to the 86 terminal and gave it ground with a power probe and the truck cranked and fired up until it ran out of fuel in the rail. This led me to believe I had a bad ECM so I replaced it today and nothing changed it did the exact same thing. Any help is appreciated!

[richard wysong]

Problem has been posted many times but few post the solution. 1 that I recall is bad connections/corrosion in the under hood fuse box, another is bad grounds which are common to these trucks. probably will take some time checking voltage drops

[JohnDeereJoe]

The fuse box is in pretty good shape in regards to corrosion and I'm hoping it just a bad ground somewhere. Do you know what the three grounds at the back of the block are for?