I have exterior lights on a timer switch. The lights are too bright. Can I add a dimmer switch to adjust the brightness? And change the timer switch to a three-way switch. Will that work?
Can I add a dimmer switch to adjust the brightness?
Yes, the dimmer would just be added in series with the timer.
And change the timer switch to a three-way switch
Normally, a timer controller goes on the feed to the circuit for outside lights without any other switches. However, you can wire things any way you have the imagination for within reason. If you connect the timer as a 3-way the other switch will override the timer anytime it is operated. If that is how you want the circuit to operate then it can be done.
A switch like this: https://www.amazon.com/Honeywell-PLS750C1000-Ti072-3W-Sunrise-Required/dp/B01IAEPFD4 Can be used as a single pole or 3-way switch.
Good luck and stay safe!