Total shutdown after 5 seconds.....

Hello All, I’m a new member & in need of help....
I have a 97 pickup with a 2000 4.3 Vortec motor. It was recently rebuilt/refurbished by a cousin (Grate mechanic) & it ran grate for 2+ weeks. Recently when I was leaving a parking lot it slightly sputtered than ran poorly till I got in the driveway. Now when I start it it runs ok for about 5 seconds then completely shuts down, everything motor & power...completely black out.It also does this when the key is engaged & engine off.

The computer had to be swapped out a few times to work properly with the motor during the rebuild & the engine harness was replaced as well.

any help is greatly appreciated...we have no clue where to start looking.


THANK YOU for any help.:)
Dave In Omaha

What all is everything shuts down?
Does dash lights shut down to?
What is the security light doing?
Does it lose spark and fuel pressure when it shuts down?
Check all battery and fuse box 12 volt power and grounds.

97 is a bad year for ign switches?
Is ign switch feeding 12 volts to everything?

my 2000 started and stalled everytime after i did a steering column and it was the security system