The OP said there was no ground wire.
Yea, the metal box might be grounded via conduit connections back to the breaker box. It’s something that can be measured.
Yes, it is probably hot. But given the fact that there’s some sketchy things previously homeowners did (stranded wire, wrapping wire under screwhead in CCW direction), I would want to be 100% sure. See my previous posts. Just run a long extension cord to a grounded outlet, and make voltage measurements vs. ground.
You… did place an order for a digital DMM from Amazon, yes? Here is one for $10.
In the house I grew up in, built in 1912 and probably having its wiring modified multiple times by various people of various qualifications over the years, all the wall switches switched the neutral wire rather than the hot wire. They worked, but of course were not wired “correctly” (nor safely). So I wouldn’t assume a wire is hot just because it is switched.
The switches in my house were also oriented so they were “on” when the switch was down and “off” when the switch was up. Those wacky guys.
That might be easier said than done. If the out let is 2 prong without a ground and there is no ground wire there is a good chance this is an older house with only 2 wire and no grounds.
But you can try checking all wires to the conduit. If and I say If you get 120 volts from a wire to the conduit then the house was using the conduit as a ground.
Wow, I did not even catch that!
Well, it is in my “save for later” folder. Does that count?
mmm
That’s the impression I’m getting, too. Grounding became code in 1962.
mmm: the GFCI is the one code-compliant workaround in this situation, but … just an FYI … you may want to consider the situation, writ large, at some point:
Having both red and black wires makes me think that there is a 3 way switch involved here.
But then the use of stranded wire plus the counter-clockwise wire under the screwhead makes it pretty clear that whoever wired this had no idea what they were doing, so all bets are off.
While I am generally all for people figuring out how to do things on their own, given the OP’s lack of test equipment and lack of experience I think calling in a skilled electrician is the best option at this point.
Normally you can assume that things were done mostly to code and can figure out from looking at it what goes where. But in this case, you need to assume that whoever did the wiring was a complete idiot and could have done almost anything. That makes troubleshooting a lot more difficult. At a bare minimum I would say the OP needs to buy a multimeter, and if the paths of the conduits aren’t obvious, I would also buy one of those wire tracers that sends RF down the line and then uses a handheld receiver to follow along the wire and trace where it actually goes.
It’d be really hard to argue with E_C_G on this one.
Further, how old IS the house? Pre-1962 almost surely means an ungrounded panel. Pre-1950 might take us into knob and tube territory – yet another wrench in the works.
Also note this quote from the link above:
(A homeowner cannot safely test a GFCI while it is in place, installed on an electrical circuit that has no ground but the GFCI can still be expected to work correctly if it is wired properly.)
Not being able to check my own work in this situation, IMHO, is a pretty big cause for pause.
One other ?, mmm: My eyes aren’t so good, but are you in Cali and is that redwood framing?
That would spell “pretty damned old” to me. Our last San Diego house had a redwood framed detached garage and that house was from about 1916.
Random answers:
First of all, I really appreciate all the input.
The house is a bungalow, built in 1950. No knob and tube.
Not in California, no redwood.
No 3-way switch.
The fact that the installer made some obvious blunders, as some of you have pointed out, makes me not want to mess with it further. I am going to leave this one to a pro.
And I will make a point to be there with them while they resolve this. There is much more I can learn here.
Finally, yeah, I am going to buy a mutlimeter, just because I should have one. 
mmm
A homeowner cannot safely test a GFCI while it is in place, installed on an electrical circuit that has no ground…
If a GFCI receptacle is not grounded, its ground-fault circuitry cannot be tested using an external tester. But the test/reset buttons on the receptacle itself will still work.
Good info in this thread, but very confusing for a beginner.
I’ve been a sparky for 35 years.
From what I can tell, the switch is on the load side of the circuit. Someone tapped the circuit in the box, added a switch and extended the wires to a light or something.
The easiest way to see if the box is grounded is to take a resistance reading from the white neutral wires (either, try one at a time) to the device box. If you get 0 ohms on either one, then you have a grounded box. This is because the neutral and the metal raceways are bonded in the electrical panel. If you don’t have a ground, you can still install a GFCI - in fact, it’s recommended on ungrounded circuits, you just have to label it as such.
Firstly, I would have simply installed a GFCI breaker (replace the one that feeds the garage) in the main panel instead of trying to rewire the garage. This should be done by a sparky though.
Lastly, from what I’ve read, you have 4 wires to deal with. Without a meter I would make these assumptions based on experience - The new pair (red and white) and the older pair (black and black/white - we will assume original wiring and will come from the breaker). The red and white will be the load and the black and black/white will be the line wiring (as applied to the new GFCI). If you tried to wire the new GFCI this way and were not successful it may be that you didn’t reset the GFCI prior to testing, or your touchless voltage sensor is shot. It looks like you have a plug in tester as well, that should have worked fine.
I see that on one of your many trials you had a green light on the GFCI, that should have been the “correct” install. Make sure the reset button is pushed in and then hit the test button. You should hear it snap and the reset button will pop out. Reset again and then plug in your tester.
With a proper multimeter this job takes 30 seconds to figure out.
Turn off power.
Seperate all wires in box so they aren’t touching.
Using the Multimeter, find the neutral that is bonded to the box (0-Ohms).
(The other neutral wire should have infinite Ohms.)
The wire that is in the same conduit as the neutral with 0-Ohms will be your hot from the breaker.
The other two wires are your load.
The above assumes you don’t have incorrectly wired outlets elswhere or two neutrals from separate circuits spliced together somewhere.
What you are going through right now, is why electricians should be involved in any re-wiring efforts.
What city is this in?
When you checked you should have hit the test button and then the reset button to verify operation. If you got the reset button to pop then you have it wired correctly. You might have to hit the buttons in this order depending on make/model - reset/test/reset OR test/reset/test/reset. I like to cycle the test/reset a couple of times to make sure the thing works.
It’s likely that you had this thing wired correctly once and didn’t know it.
I believe this is probably true.
In my case I have one white, one red, and two black. I am assuming that I would take a resistance reading from the white and again from the red?
Would this only work if the box is grounded?
Suppose I do not get 0 ohms on either the white or red wire, how should I proceed then?
mmm
@Uncommon_Sense, I would really like your input on this question:
Probably, but I would still test this with the Meter to be certain that something goofy isn’t going on with the wiring (like the colors are all jangled up and the switch is actually switching the neutral or something). With out verifying what are actually the neutrals and/or the hots - we are speculating.
However, if we assume that the red is the (switched) hot, then yes you are correct. AND we also assume that the white is the real neutral then - the red would be the LINE hot wire and the white will be the LINE neutral. The black wires will likely be as follows: the one that was on the left side of the (old) 2 wire outlet will be the load line, and the one that was on the right would be the load neutral.
To simplify, you have 4 wires on the GFCI, (2) neutrals (line and load) and (1) switched line and (1) load line.
I know you are trying to figure this out on your own and you are almost there, but this is the sort of situation where it usually is cheaper in the long run to have just got an electrician in the first place. No I told you so, just communcating where Ive gotten with this sort of stuff.
I am no electrician, I’m a general contractor / carpenter. I had thought that conduits were grounded, but maybe not in old systems. That being said, it is relatively easy to upgrade an old outlet to grounded by adding a run of 14 gauge to the nearest pipe / buried chunk of metal. Usually ive left this up to the electri ian, but its a pretty simple procedure.
There are really a good number of important caveats to that old-school approach:
One thing to consider is the possibility that parts of the plumbing system either have been, or will be, repaired or replaced by plastics. Even just a fitting here or there could cause problems in certain circumstances.
Conduit should be grounded because it should run from the electrical box to the main electrical panel box. But what can happen is a loose fitting or a fitting becomes corroded breaking that ground.
Depending on the condition of the conduit and how it was ran it may be possible to pull a new ground wire through the conduit back to the main panel. But it would be best to have an electrician check this out and pull the wire.
I may be wrong but by the picture that does not really look like conduit, but may be pipe.