how do I know whats wrong with my abs...

my light turns on after driving it for a wile...
I just bought the car about a weak ago...

I cleaned the abs censors with a clean rag no solvents or anything but the light still turns on

Is there a way to bring up a code for that or is this to old of a car to that that on..I know its not an obd 2 ro what ever but were can I find that info?...thanks..