If the ignition switch is faulty it could leave an electrical component turned on and that could potentially cause a dead battery. That would not necessarily be the case and you might notice if the switch is supposed to be off but something still runs.
How do i change the ignition switch in a 1988 Chevy camaro
how to replace an ignition switch for 2005 chevy equinox
How to remove ignition switch
I would expect that the power for the fuel pump would be supplied through the ignition switch so I would start there, that is check the ignition switch.
Remove the retaining ring at the top of your 1985 Chevy ignition switch. Slide the ignition switch out and remove the wiring harness. Reverse the process to install the new ignition switch.
Begin by removing the retaining ring at the top of your 1992 Chevy ignition switch. The ignition switch will slide out. Remove the wiring harness from the end of the ignition switch. Reverse the process to install the new ignition switch.
Remove the retaining ring from the top of your 1989 Chevy Corvette ignition switch. Slide the ignition switch out and remove the wiring harness.
You will need to remove the ignition switch retaining ring in your 2002 Chevy Astro Van. Slide the ignition switch out. Remove the wiring harness from the end of the ignition switch. Reverse the process to install the new ignition switch.
Remove the retaining ring at the top of your 1994 Chevy Corsica ignition switch. Slide the ignition switch out and remove the wiring harness. Reverse the process to install the new ignition switch.
The large red wire is the battery or hot wire.
Remove the retaining ring from the top of your 1999 Chevy Cavalier ignition switch. Slide the ignition switch out and remove the wiring harness from the end of it.
You will need to remove the retaining ring from the top of your 1997 Chevy Camaro ignition switch. The ignition switch will slide out. Remove the wiring harness. Reverse the process to install the new ignition switch.