All grounds together in the box.

Whites 3, 4, and 5 together in the box.

Black 4 to Black 2.

White 1 to White 2.

Red 1 to Red 2.

Black 1, 3, and 5 together in the box.

This is a violation of the 2014 NEC I believe, as there are no neutrals in your switch boxes, and you basically have 2 "dead end" 3-way switches. Not sure if this applies to residential though, as I do primarily commercial work. Someone feel free to correct me if I'm wrong.

Hope this helps.

Thanks for the reply. The codes aren't my expertise, so if I need to change the setup to make it compliant I'm all for it (especially since I didn't wire the original circuit).

I previously had the box wired exactly as you described above, hit the switch, and the breaker immediately tripped. In the process of troubleshooting, I took the ground wires going to both lights (Ground 3 & 5) out of the bundle... still tripped. I then took the box ground (Ground 6) out of the bundle (leaving only Grounds 1, 2, & 4) and the lights work as intended. I'm admittedly stumped.

Does the circuit trip with grounds 3 and 5 (your switch leg grounds) tied in, minus the box ground?

Are you sure that the black wires are both connected to the Common terminals on the switches and that the ground wire are not inadvertently in contact with any bare wires or terminals?

As for no neutral at the switch, I believe an existing circuit would probably pre-date this relatively new requirement, which not all jurisdictions have adopted.

I admittedly did not try just isolating the box ground from the bundle to see if that was the culprit. If that configuration did not trip the breaker, what would that indicate?

As far as the switch wiring... both black wires are on the common terminals. The only part of the circuit I changed was in the junction box - since it worked fine prior to installing the new lights, I can only assume it's something in the box giving me problems. The ground wires in the box are isolated and not inadvertently in contact with anything.

I'd next check the light fixtures with an ohmmeter for an internal short.

"I admittedly did not try just isolating the box ground from the bundle to see if that was the culprit."

Well, check it. I am going to assume you have a metal octagonal box with nonmetallic sheathed cable running into it. First, you have too many wires in the box if it is a standard box. Second, you might have two cables under one clamp in the box. If someone tightened the clamps too tight, especially if there are too many cables in them, and then someone forced too many wires into the box, you could have enough damage to a hot wire's insulation at the clamp to cause the problem.

Make sure that the metal of the light fixture over the box is isolated from the metal junction box as well, or you would be shorting out through an alternate route.

The box is not a standard box - it's a large square box to accommodate all the connections, mounted to a ceiling joist. The light is also mounted to a ceiling joist but is 2' from the box, so the two are not touching.

Will isolate the box ground from the circuit and test it, although if it turns out the box ground is the culprit, I'm curious as to why grounding the box trips the breaker.

Grounding the box will only cause a breaker to trip if the light or the wiring itself is defective. This is a safety feature, not one to circumvent by disconnecting the ground.

Does the breaker trip when the switch is cycled and there is no fixture attached? If so, you may have a nail or something penetrating the cable and in contact with the hot lead and ground/neutral.