I'm using a Leviton 1755 combo 3 switch for a bath light/fan combo and then onto a vanity light. Basics: wires from ceiling light/fan: black, red, white, ground. Wires to vanity light: black, white, ground. 1755 Switch has common hot connection on right and 3 load connections on left. How do I wire this up? Currently I have only 2 switches wired: incoming black to right side(common hot), white to switch 1, red to switch 2. Light (1) OK, Fan (2) only on when light (1) is on. Now I want to add vanity light to switch 3 by continuing on with new wire black,white, ground. Please help, I am stumped!

Try the link below for a diagram.
I would think that you have one black feed and two black legs going out, and three common wires that should be wired together with a wire nut. Is this for a ceiling fan with a light? or ?

1) Copy following link to see wiring diagrams:
http://waterheatertimer.org/How-to-wire-switches.html#triple

2) There are two basic wiring type, depending if power wire and neutral arrive in switch box first, or power wire and neutral arrive in ceiling box.

3) Most homes, the power wire is in ceiling box.
In this case, a minimum of 4 wires are needed between ceiling box and switch.

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

The switch that you have works like 3 seperate switches. most of these switches will have gold screws
on one side and silver screws on the other side, lets say that the left is gold and the right is silver, and
the switch may also have a green screw for ground. your 12/2 with ground is your main hot, you may
want to mark it with a piece of tape, so you know it's the incoming hot. the ground off your hot will tie,
to the green screw on switch and continue and tie to your vent light which should also have a ground
the white coming off the hot is your neutral, it will go straight to your white or whites on your heater.
the black hot wire at your switch will go to each gold terminal on one side of the switch,there are two
ways you can do this, go to one side and just run a jumper, or put one wire on each gold screw and
tie in to your hot-black wire with a wire nut. now for the switch legs, you will need to run from your, switch
to your heater either another pair of 12/2s or a 12/3, each side of the switch that has one silver screw,
it's easier with a 12/3 normally a 12/3 will have a red,black,white,and ground.
top switch red to red on heater,black to black on light and the white blue on the vent,so from your switch
to the heater you would have to run a12/2 you would not use the black only the white and ground.
remember the white-neutral coming from the switch will be tied to all the whites at the vent,light,heater
except for the 10/3. the 10/3 is used stricktly for the switch legs. good luck!

1) Leviton 6515 is incandescent only:
http://www.amazon.com/Leviton-6515M-I-2-5-10-15-Electronic-Incandescent/dp/B0007NOZDI

2) Below is list of countdown timers with horsepower rating so they work for fans:

GE15088 countdown timer is rated 3/4 hp
http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay

Intermatic spring wound countdown timers are rated for 2 horsepower
http://www.intermatic.com/products/timers/in-wall%20timers/decorator%20spring%20wound%20timers.aspx

Woods spring-wound countdown timer says bath/ ceiling fans, but doesn't give horsepower
http://waterheatertimer.org/pdf/Wood-59700-series--spring-wound.pdf
http://waterheatertimer.org/Woods-timers-and-manuals.html#countdown

Woods push-button countdown is 1/4 horsepower
http://www.amazon.com/Woods-59014-Decora-12-8-4-2-12-Hour/dp/B002C54GH4

Wattstopper RT50 at Grainger shows 1/6 horsepower rating
http://www.grainger.com/Grainger/WATT-STOPPER-Time-Switch-2HTE1?Pid=search

3) Following timers are NOT rated for fans:

Lutron MA-T51 countdown timer specifically says it cannot be used for motors.
http://www.amazon.com/Lutron-MA-T51-WH-Maestro-Countdown-Timer/dp/B001EFV1DA
http://www.lutron.com/TechnicalDocumentLibrary/0301041A.pdf

Pass and Seymour RT1 countdown does not show rating for horsepower, so this timer will probably not work for fan motor
http://www.homedepot.com/Electrical/h_d1/N-5yc1vZ1xg8Zarcd/

Question needs more details. Let me answer as if you have one light and one switch, and one cable coming into switch box from ceiling.

Usually a switch-dimmer combo operates 2 different Loads (lights).
One light is controlled by switch, other by dimmer.

If power source is in ceiling, then one cable enters switch box.
Cable has black, white and ground wires
Old switch had 2 brass screws where black and white wires connect
Black wire brings Hot down from ceiling, and white wire connects back to Load (fan).
Neutral wires are in ceiling box, and not inside switch box, and are discussed.

With new dimmer: Black Hot wire from ceiling connects to dimmer black wire.
White Load wire connects to one of the red wires.
The other red wire goes to another Load, which is unknown at this point.

Add a comment for more free help. Say what cables and wires enter box, and what Loads you are controlling. Also add exact model number so expert can reference manual. Levition instruction sheets and manuals usually have toll free number.

Also take advantage of fixya expert assistance live.
For a price, expert works with you via e-mail or phone while you work on circuit or any do-it-yourself project.
Fixya is always less expensive than a service call.

1) Look at screw color.
New device has brass screws on one side, and 1 silver screw for each switch located on other side of device.
Hot wire goes to brass screw.
Wire to fan goes to one silver screw
Wire to light goes to another silver screw.
Wire to heater goes to another silver screw.

If you do not have a wire for each individual Load, then you will have to add wiring.

2) Electricians don't guess, they test.
Separate wires for testing.
Turn power ON.
Test each wire to bare ground wire.
Tester lights up on Hot wire.
Hot wire connects to brass-colored screw.
If any wires on old switch was connected to same Hot wire, then also connect that wire to brass-colored screws.

Hot wire is identified.
Test Hot wire to each other wire in box, except bare ground.
Tester lights up on Neutral wire. Neutral wire will NOT connect to this switching device.
Next, connect one of the remaining wires to a silver screw.
Turn power ON.
Flip switch to see what Load that wire controls.
By process of elimination, add wires to each silver screw and test each by flipping switch.
Breaker will trip if you connect Neutral to silver screw.

Add a comment for more free help.
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For a price, fixya expert speaks with you over phone while you work on circuit.

Leviton triple switch
Nutone P66V

Nutone looks like an ordinary three-switch combo being marketed as a bathroom 'fan switch.'
The screws on the device would tell the story.

Look at the Leviton screws:
The switch has dark-colored screw on one side >> the hot from breaker always connects to dark screws.
Other side of switch has 3 silver-colored screws, but these can be brass colored screws > the wires to fan light and heater connect to each of these screws.

Most likely the Nutone switch is identical to the Leviton
I say this because the descriptor on Amazon describes it as a 'fan' switch.
It's being marketed as a bathroom fan-light combo switch >>> so it looks like an ordinary three-combo switch

Sounds like it to me that the netual is not there.

Switch will have a commom terminal that the hot wire connects to.
The other three terminals are for the devices -- light, fan and other device.

The white wires should be the grounded wire returns for the circuits unless they are identified by color tape to be hot line side of power.

Be careful of the grounded side of circuit, can shock or kill, treat all wires as being energised. If you are not sure, use a electrical tester,
or get help.