I recently bought a home built in 1940's and am doing some remodeling. I unhooked my bathroom light fixture that hung above the mirror and found that the wires were not color coded as I had expected. Of course in my hurry I did not label which wires went to what on the original fixture. Now I am faced with two black wires and 1 red wire coming out of the wall. My new fixture has the typical white and black with bare ground. Any suggestions on how I can know which is hot, neutral and ground? My last resort would be to call a professional to come over.

Use the sink as a ground, use a voltage tester across each wire to the sink, you will find which is hot.

Or there are non-contact testers that you only need to hold next to a live wire to find which is hot.