I have a 99 durango and a abs light came on

Check the speed sensors maybe time to change

Could start by checking the level of the brake fluid reservoir if low check for leaks. Also check if the parking brake is not applied. If those things are ok then check folloowing. 1) make sure the brake shoes/pads, calipers and wheel cylinders are in good condition 2) Check the electrical connectors at the control module assembly 3) Check the fuses for the ABS. 4) Follow the wiring harness to the speed sensor and valve and make sure all connections are secure and the wiring isn´t damaged. If all of the above checks out fine it is most likely the sensor or sensor depending if you have 2 or 4 w ABS system then it is best to take the truck to a dealer or a shop you trust to have it diagnosed properly.