2000 Ram ABS & Brake light on

From : dingy101

Q: 2000 dodge ram 5.9 auto 4w abs abs light & brake light is on i have checked fuses swapped pertinent fuses & relays with same ones in different circuits lights came on & i found front brake pads needed replacement replaced pads but did not correct lights cruise control works & speedometer works fine. front wheel sensors & cables appear ok. i have disconnected battery to clear computer. could rear sensor be defective with speedo & cruise functioning any suggestions what is purpose of the relief valve located on top of the combination valve gary .