This light came on IMMEDIATELY after I had a custom stereo installed. Of course, the stereo guy said the ABS light has nothing to do with what he did. However, I have to go back because one of the speakers is already not working, so who knows.

abs........usually a sensor, either out of line or needs replaced.
when the stereo guy was messin around with wiring might be something he did accidental but not probable

At first I was gonna tell you that the ABS line was probably not functioning properly attached to your lower strut. After you said It happened immediately after the Installation, I'm convinced that the Installer crossed either two wires, or shorted something out In the electrical system of your car In total. Dont be fooled, that's probably just something you see, there may be other problems that you cant see like brake lights, reverse lights etc. I would have the tech just go over everything, but before you get Into depth.. Check your fuses. Good luck, Botts..