If i bundle all white wires together and install the black wires on the provided terminals on the side of the switch,what wire gets attached to the common terminal?

Well black is usually ground or negative. The chassis provides a common ground so it could have been attached to the frame.

Hi Sara,

Please read this entirely before attempting.

I am an electrician and would like to help you with this problem. You have provided great detail of your situation, yet I am confused about the statement describing how you wired it:

"-Red Wire (used in 3-way installation-tagged) from switch to the red wire in wall."

Before checking wiring, be sure to shut off the power to the circuit.

The "tagged" wire should be the one you identified with tape (when you removed the original) that was connected to the dark colored (called a "shunt" or "common terminal") screw of the switch.

In a 3 way installation, both red wires from the dimmer switch are used. In a single pole installation, only the UNinsulated red wire is used and the insulated wire is not.

To which wire do you affix the "tag"? If it was a short wire that ran between the the bundled black wires and the shunt terminal screw of the old switch, then the dimmer switch's black wire should be combined with these bundled black wires. One of the dimmer switch's red wires would be connected to the red wire in the box and the dimmer switch's last red wire would be connected to the remaining black wire in the box. I understand that this is the way you have it currently wired - but without being able to dim.

If this is all correct, did you check / change the Minimum Brightness Adjustment setting for the switch as detailed in Step 7 of the directions?

"This Dimmer incorporates a
minimum brightness adjustment
that allows you to set the level of
light when the slider control lever is
in the lowest position.
Move slider to the lowest position.
Using a small, insulated screwdriver,
rotate the adjustment screw as
shown until the desired level of
minimum brightness is obtained."

I hope this helps and good luck!

You are attaching your light to an outlet?
Are you talking about ordinary double 120Volt outlet where you plug in lamps?

Or are you connecting your light to a switch?
If you don't have a switch, then the light will be ON all the time.

Usually if the light has 2 white and 2 black wires, then you twist together both whites and twist together both blacks.
If you are connecting to ordinary 120volt outlet, then the outlet has black wire(s) on one side connected to brass screws, and white wire(s) connected on other side to silver screws.
Attach black to black and white to white.
http://waterheatertimer.org/How-to-wire-switches.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

You are attaching your light to an outlet?
Are you talking about ordinary double 120Volt outlet where you plug in lamps?

Or are you connecting your light to a switch?
If you don't have a switch, then the light will be ON all the time.

Usually if the light has 2 white and 2 black wires, then you twist together both whites and twist together both blacks.
If you are connecting to ordinary 120volt outlet, then the outlet has black wire(s) on one side connected to brass screws, and white wire(s) connected on other side to silver screws.
Attach black to black and white to white.
http://waterheatertimer.org/How-to-wire-switches.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

The 2 whites from the Romex cable go together along with a jumper. Now, the neutral jumper from the white bundle goes to the SILVER screw terminal one the side of the outlet where the LONGER slot is.

The black wire (load/light side), goes to the brass screw terminal on the SAME side outlet.

The OTHER black (line/HOT) wire goes to the opposite side of the switch, the side that has the connecting tab.

The grounding wires go together and then get connected to the box ground.

You have almost got it, but the wires aren't separate the correct way. On one side of the device your going to have your power. The side that's power will have two brass colored screws. You need to find your power wire and splice two wires to it then connect those two wires to your device on the power side this should leave you with two wires. If you happen to have two white wires now, you are going to splice them together with a third wire (called a pigtail just as you did with the blacks on the power side). Now on the non-power side the screw colors should be brass and silver. You will attach your white wire or bundle of white wires using the pigtail to the silver screw. This is the neutral for your receptacle. Then the black that goes out to your light will get attached to the brass screw. The problem you had was then a neutral was being attached to the switch as well as the receptacle and a switch requires no neutral, a switch is simply a break in the power line.

If the timer is already installed, then the incoming (from the breaker or source) black wire should be connected to the #1 terminal. The incoming white wire should be connected to the "A" terminal and the bare (or green) wire should be connected to the "GR" screw on the (lower) case.
To connect the pool filter (load) to the timer, connect the black wire to terminal #2, the white wire to terminal "A" (along with the incoming white wire) and the green wire to the "GR" screw (along with the incoming bare or green wire). Usually one twists the two green or bare wires together with a short pigtail using a yellow or red wire nut and then connects the pigtail to the "GR" screw.
The two white wires don't need to be pigtailed, as the "A" terminal is designed for two wires.

First, turn off the circuit breaker. The three wire bundle should be the incoming power, the four wire bundle should be going to the fixture. Using a duplex switch (one with two toggles), the incoming black wire goes to one side of the switch, the outgoing black and red wires go to separate terminals on the other side of the switch. The whites are connected together. The Grounds (or bare copper) are connected together and to the switch ground screw. Hopefully both the outgoing read and black were connected to the old switch or you may have to rewire the fan to wire up the fan and light separately.

To add to red54's comments:

This is what I believe you have:

- one source in the ceiling box (black & white)

- one donwline circuit in ceiling box going to another wall/ceiling box (black&white)

- on switch wire in ceiling box coming from your wall switch (black & white) -- this is the white wire which will be hot when the switch is truned on

Here's how it should be connected:

- all 3 blacks in ceiling box connected together -- no other wires in this bundle

- white wire (which is hot when switched) coming from switch connects to the black/blackwhite fan wires

- connect all reamining white wires together in bundle

- connect all ground wires together

It's that simple. Trick is figuring out, of the three cables in the ceiling box, which is source, which is downline, which is switch.
Maybe red54's procedure can help you figure that out.

You are correct.