Where did I go wrong with my home wiring issue?

I had a typical room from the mid 70s with nothing but a switched outlet. I've installed 4 overhead, recessed LEDs that I want to control with that switch, converting the formerly switched outlet to "on" all the time. The switch box has power for lights in adjacent rooms as well that are not controlled by that switch and simply run/connect in that box.

I ran my new romex (12/2 is what I had) to the box, and connected that new wire to the lights. The wire between the switch and the formerly switched outlet appears to be 12/3 ( black, white and red wires). It was not a 3 way switch, so not entirely sure why 12/3 was used.

I connected all grounds (bare copper) together. All neutrals (white) together. And all of the original hot wires (2 blacks and 1 red) together in the box. I ran a pigtail from the hots to the switch, and then connected the hot from my new wire to the switch. All wires appear to be well and fully seated in "push style" connectors.

With it wired this way, my formerly switched outlet is "on" all the time as desired, and all of the lighting in adjacent rooms works as intended. However, when I attempt to turn on the new recessed lights with my switch, it trips the circuit breaker and kills it all.

I'm guessing that I may need to do something different with the red hot wire from the 12/3, but what? And if that's wrong then why does it all work as long as the new lights are switched "off"?

Here's an idea of what I did in the switch box:

Here's the previously switched outlet (I didn't change anything here, just for reference in case something seems odd)

Sounds like you have a short in one of the new lights, or the wiring to them.
 

I don't think the red wire has anything to do with it. 

I agree with SV reX, one of your new lights has an issue. Go through and check for obvious signs, wire not in wirenut, something discolored  if nothing jumps out. Disconnect three from the circuit and try turning on. If that one works, reconnect one at a time until it trips again and that is where the problem is. May be a loose wire or could be a bad fixture. Leave the switch or breaker off when checking/making connections Your red and black wire splice is fine.

I will disagree with the others.  Try disconnecting the red wire and see what happens.  It's not that common to have a bad fixture out of the box, it happens but not often.

In reply to triumph7 :

The red wire is feeding the outlet, and no changes were made there. The red wire is not attached to the switch, and the breaker trips when the switch is flipped. 
 

You're right it is uncommon for a fixture to be bad, but it's not uncommon for a connection at the fixture to be bad, or a wire going to the fixture to have snagged on a nail. 

There is one advantage to disconnecting the red wire at the switch...

If the outlet still works, then it's not the same red wire. That would be useful to know. 

Ok. Well, it's nice to hear that my approach probably isn't completely wrong. I'll double check the light installation to make sure there are no issues.

If nothing turns up there, is a failing circuit breaker a possible issue? The breaker seems to function normally but I'm also assuming that it's from the mid-70s like the rest of the house.

99% not the breaker.  It is something you did.  You will probably have to work backwards through your process.  Many times when a lot of wires and connections are crammed in one wall box things touch.  I would pull all those wires out and spread them looking for missing insulation, etc.    

With you having them spread apart, maybe have someone else flip the breaker on while you watch/listen to the open box.  Sometimes you'll hear or see the spark.  If the breaker doesn't pop when you have everything spread apart, that would tell you something.   

I suspect it has something to do with the fact there are two positives (red and black) in one box.

A volt meter will be your friend.

In reply to STM317 :

There is a possibility it's the breaker.  If there are other things loading that circuit and adding those few lights overloads the circuit, then it's possible. 
 

But very unlikely. 

Not much chance of a failed breaker. The switch is throwing a dead short into the system. 

Step 1- buy a tester that will show voltage output. 
 

Step 2- disconnect all the hot wires- the blacks and the reds.

Step 3- check each hot wire.  Only 1 of them should be hot, and it should be 120V.  If more than 1 is hot, you have 2 circuits.
 

If the hot wires are 2 separate circuits, put your tester across both hot wires.  If it reads 240V, you have 2 circuits and they are on different busses on the panel.

I think you will find only 1 hot wire, but it's worth checking.  If there is only 1 hot wire, put it all back together. Your problem is not the wiring. It's in the lights.

If there are 2 hot wires AND together they read 240V, then you ran 240 through your lighting circuit.  Your problem is still in the lights, but you fried your LEDs and created a short.

The short is in the lights either way. 

In reply to SV reX :

If there are 2 hots together, and flipping the switch sent 240v to my new LEDs, wouldn't it be sending constant 240V to the lights in the adjacent rooms too? They're all connected together in the switch box, and the other lights and outlets seem fine as long as the breaker hasn't been tripped.

I couldn't get a pic with my voltmeter, but the basic outlet tester says everything is fine with the outlet that was formerly switched:

In reply to STM317 :

Yes, that's true. But the new fixtures may be more sensitive, and shorted out first. 
 

I don't think that's the case. I think it is wired fine, and the problem is the new fixtures. I just suggested it to rule it out. 

In reply to STM317 :

There is nothing wrong with that outlet. You didn't change anything. 
 

Im offering concessions to those who are suspecting the red wire. These are the diagnostic procedures to rule out issues with the red wire. But I don't think there is any issue with it. The problem is a short in your new fixtures. 

Here's what I think the red wire is...

The 120V feed comes into the switch box. 1 black wire.  They used it as a junction to feed the next room. 
 

They wanted a switched outlet, but that outlet also feeds other outlets they didn't want switched.  So, they ran 12/3 from the switch.  Black leg hot, red leg switched. 
 

Inside the outlet you should see a 12/3 and a 12/2.  The whites are tied together (on the outlet).  The blacks are tied together (feeding the hot leg through to another box).  The red leg is switched and tied to the outlet. 
 

Nothing wrong with that wiring.  They used the switch box as a junction box, which is unusual, but there is nothing wrong with it.

The problem is still in your new lights.  

You can trace the issue in the new lights like this...

At the switch box, disconnect the white wires from each other. Flip the switch, and it may not trip the breaker. Leave the switch on, and put your tester on the white wire from the new lights. The white wire will read hot if  it's shorted to neutral in the lights. 
 

If the breaker trips when the whites are disconnected from each other, then then short is to ground. A black wire is most likely touching the housing of a new fixture. 

In reply to SV reX :

Depending on the power supplies in the LED it may still read voltage on the white when tested because it may pass through the windings in a transformer. 

I'm wondering if there isn't something funky going on like a switch leg run through a white wire. 

Was the receptacle pulled and wiring on that end of the 12/3 verified? 

In reply to Toyman! :

I guess I'm missing something. The pictures show every wire. I see nothing abnormal. 
 

The switch is wired from the hot, and tied to the lights hot.  The white is also tied to the lights neutral. Everything works fine until the switch is flipped.  When the switch is flipped, it's a dead short.

I see nothing difficult here. The hot to the lights is shorted after the switch. 
 

Transformers, switched neutrals, dual hot legs are all over-thinking it. 
 

Imgon described earlier how to trouble shoot the lights.

GRM pulls through again (there was never any doubt). With some confirmation that I hadn't royally screwed up anything in the switch wiring, I got down to troubleshooting the lights. There was a bad connection in the first light that I tested. Fixed in less than 5 minutes. Thanks to all for the help!!

In reply to STM317 :

That's awesome!  Congrats. Thanks for the update!

Svrx - Hurry up and open up your own business!!

In reply to jfryjfry :

Haha!  I'm working on it!

A sketch or two would greatly help in understanding what you had, and what you did.

Personally, I'm curious about that red wire.  What it was doing before, why you wired it in hot, and what's on the other end.  
 

Which, to me, begs the question of did you have a two way switch and circuit on that room?  And if so, did you continue to use it, and accidentally wire the ground to the other hot leg of the switch?

In reply to foxtrapper :

I think SV rex described the situation pretty well:

In reply to foxtrapper :

It was a switched outlet, not a 3-way switch.  By wiring the red wire in hot, he just made the outlet so it is no longer switched.  He could have done it with the black hot leg and abandoned the red wire.

Grounds and neutrals are never wired to 3-way switches.  Only hots (and traveling switch legs with the potential to be hot).