I'm replacing an overhead light with a ceiling fan in a 1940's house. The wires are not color coded & my multi meter reads 120v coming from ALL wires to the ground! How do I find out which is the hot wire? They all read hot! There are 2 wires twisted together, a ground wire and a solo wire. I tried hooking it up both ways & the breaker flipped off each time. ALso the light has a dimmer wall switch- I assume I have to change this for the fan to work.

If the breaker tripped, it may have destroyed the dimmer, remove dimmer, hook fan up, then connect the 2 wires at switch to test before installing a fan control to insure correct wiring before destroying new fan control.
Can you say what color of wires you have(All black, all white, or what?)
Can you say how many wires coming in from each opening?

How was the overhead light wired?

Ceiling Fan Wiring, Ceiling Fan Wiring Technical Help, Do it Yourself (DIY) - Ceiling Fans N More (http://www.ceiling-fans-n-more.com/ceiling-fan-wiring.php)