Electrical
 

Presently have a three way switch in my hallway.
I would like to Change one toggle switch to dimmer so I can decrease lighting is this possible? Do I need a 4 way switch ?

You can purchase a three way dimmer switch to replace the three way switch you have.

There are quite few differnt style of three way dimmers on market but for now are you just replaceing with one three way dimmer and second switch as conventail three way switch ?

If so it pretty easy to do it however there is one more step you will have to pay attetion is common screw that typically darker colour screw than other two screws which typically bright brass.

The common will also marked as " C " so it will be either way and also I will advise you swap one conductor at time so it will not get this mixed up and final part make sure you have breaker off before you do this.

Merci,
Marc

Ive put the three way switch in, now one of my switches turn the light off but the other two switches will not work in turning it on?
Did I get the wrong color screw?

Certainly sounds like it.
Pics work well for the pros to trouble shot your problem.

Other 2 switches? So you have 3 switches controlling this light?

Maybe but what type of dimmer switch you have so we can able help ya on that.

Merci,
Marc