As this receptacle is very near GFCI receptacle 3 which seems to be properly grounded, I'm thinking to just run an external ground wire from receptacle 3 to receptacle 4 and everything should be all set. I think GFCI receptacle 4 is behaving as a properly wired, but not properly grounded GFCI receptacle should behave with a GFCI outlet tester. I think GFCI receptacles 2 and 3 are fine and are behaving as a properly wired, properly grounded GFCI receptacle should behave with a GFCI outlet tester. GFCI receptacle 4, model 2: lights up | OFF | OFF | RED | indicating BAD GROUND. Pressing the GFCI button successfully trips the GFCI and the lights then switch to | OFF | OFF | OFF | indicating OPEN HOT (or no power?). GFCI receptacle 3, model 1: lights up | OFF | GREEN | OFF | indicating CORRECT. GFCI receptacle 2, model 2: lights up | OFF | GREEN | OFF | indicating CORRECT. Pressing the GFCI button successfully trips the GFCI and the lights then switch to | OFF | GREEN | OFF | indicating CORRECT (this doesn't make sense to me). GFCI receptacle 1, model 1: lights up | OFF | OFF | RED | indicating BAD GROUND. Of these four, two are one model, and two are another model (I'm mentioning this in case different models of GFCI receptacles might have different behaviors). I've got four GFCI receptacles connected to two breakers. I'm using a Commercial Electric GFCI outlet tester, like this one: Since the receptacles are all outside, the wiring to these receptacles runs underground, and I have no idea what junctions (or lack thereof) have been made. The problem is that this is an old house, and I'm not really sure what is happening between the receptacles and the breakers. I'm trying to figure out what might be wrong with some exterior GFCI receptacles that I have.

Gfci outlet tester