There is a ceiling box that has 2 white, 2 black, 2 red and a ground. I want to hook up another light there that has no ground. There are two wall switches, one of which has a dimmer on it. I can get the light to work from one switch when I have one certain white and one certain black hooked up to the light but the dimmer switch does not work at all. How do I need to wire the box? Your help is appreciated. Thanks

Assuming that the 2 black, 2 white and 2 red are in two cables, that is one black, one white and one red is in one cable and the other black, white and red are in another cable. Also assuming that the switches are 3-way switches.
Assuming the black and white you are presently using are in the same cable.

What you have is a set of 3-way switches with the travelers passing through the ceiling box.


The white that you are using is the neutral. The black that you are using is one of the travelers. That black and the red in that cable should be connected to the travelers going to the other switch. The travelers going to the other switch SHOULD be the white in the other cable and either the black or the red. The only way to tell which is a traveler and which is the return wire is to pull the switch.

In one switch box you should find at least one 2 wire cable and one 3-wire cable. The black of the 2-wire cable will be connected to the switch. The black of the 3-wire cable will be connected to the switch. The white of the 2-wire cable will be connected to the white of the 3-wire cable. This is not the switch you want.

In the other switch box (probably the dimmer) you should find only a 3-wire cable. The wire connected to the common terminal will be the return to the ceiling fixture. The common terminal will be the darker colored screw (most likely black) and will be marked.

Back at the ceiling box, connect the neutral (the white you are presently using) to the white of the light fixture. Connect the return wire from the switch (in the other cable) be it black or be it red, to the black of the light fixture.

Connect the black you are now using to one of the wires in the other cable. Doesn't matter which. Connect the two remaining wires together.