battery drain problem

I will admit electrical is not my forte, but.... I would start by having the battery tested and make sure it's holding charge... If it's not the battery it's likely a small current drain somewhere. With the key out, start checking for current flow thru the fuses... (pull the fuse and read current between the sockets) I'm not very good with electrical and I can't remember what expected for total current drain. I think like 300-600 milliamps (.3-.6 amps) is expected, but I'm likely very wrong with those numbers. Hopefully someone else knows better numbers. If you find one that is drawing current then you have a starting point for finding the problem... (In my experience it's usually some sort of convenience light (in glove box, trunk, ect) that is suppose to turn off automatically but isn't.)

this happens to me with my 2002 blazer, sometimes when I turn off motor I hear a slight elec.hum. , which was killing battery, now when I shut off I make sure there is no hum, and if ther is I restart and shut down until it stops, I know it is no fix, but it keeps batt. alive

Oil pressure switch(3_wire) has contacts in it for fuel pump, these sometimes stick and the fuel pump continues to run with key off, replace oil Seder unit