Why would the anti-lock brake lights be on?

I had this problem with my Chevy Venture van after I did work on the gas tank. I thought I might have damaged a wire. I did some research and found out more on how it worked. Anti-lock brakes work by using sensors on each wheel to measure the speed of the wheels. for a detailed explanation, check a site like howstuffworks.com What i learned said the anti-lock brake light comes on if there is a problem in the system. Mine turned out to be a disconnected plug to on of the sensors. Hope that helps. When the comes on and stays on, it is telling you that it is not operational. While you mechanical brakes and parking brake will still work, the ABS will not. There can be a multitude of possible problems. There may be a bad sensor, a bad connection as listed above, a bad harness, or worse of all a bad ABS module. Lack of brake fluid flushes seem to play a factor in the fialure of these expensive little animals. It is not uncommon to see the units costing $1500.00. I am a firm believer in Anti-lock Brakes. If I didn't have them one particular evening, I wouldn't be here typing this out today.