My daughter away at college has the '99 Suburban. It is continually having a dead battery. Since trying to "repair" "long distance" I had her get a new battery installed. Battery is still draining.
Years ago the feature that would delay dome lights going off after exiting the vehicle failed. That would drain the battery. I could never figure out why and even replaced the headlight switch (from wrong advise). I resorted to using the dome light override button which keeps the dome lights of at all times.
I had her check and see if the dome light override button was engaged. It was. I also had her check that the dash light "wheel" was not turned "up" to the point the dome lights were "commanded" ON, even if not lit. That was OK. I also had her check to see if any map lights were turned ON. She says none are.
She says after a jump start the volt meter reads a little over 14 volts. This leads me to believe the alternator is charging.
I asked if the brake lights were staying ON. She said, no, she would have noticed that.
She is coming home tomorrow just for the day, Dentist appointment. So I have one day to look at it.
I plan to check, maybe remove the fuse(s) for visor mirror lights, under hood light (if it has one). Check alternator belt tension.
Any ideas? Radio gone bad? always has power for the clock?. Keyless entry? Trailer brake controller? How do I check? Any ideas?