Dad's 2007 3500 5.9L, 6 speed 4X4.
This is what happened: the headlights turned on (with the switch off) and lost power to everything else (radio, gauges, etc). Turned truck off. Now it won't crank over.
When the ignition is turned on nothing happens on the dash, its just dead. No gauges or lights. The only thing that happens is the grid heater turns on.
All the fuses are good.
I checked voltage and the fuse labled pwr-ign (#33 I think) only shows 1.63 volts. I also checked the large pink/yellow wire under the hood and under the dash and it has the same low voltage.
I replaced the ignition switch with no luck. I am thinking the TIPM or ECU but don't know for sure. I can't check the dash for codes because nothing happens, and I don't have a scanner.
What should the diagnosis process be for this?
Thanks in advance.

 

Also, I check each battery disconnected and connected and also checked with ingnition on and in the crank position and everything seemed fine.

 

are the batteries good? are all the ground wires hooked up, coming off the batteries?
Check your connections at the PCM. I had similar issues. the connections there don't have a real good clip to retain the connection to PCM.

 

Ground problems create strange electrical issues