1999 Dodge Ram 1500 5.9L 4x4 with abs and brake light on. Already changed the sensor on the rear differential and fuses under hood. What can be my problem????

 

Welcome to DF

First thing you need to do, is scan the ABS module for codes and post. The problem could ABS module main fuse relay. But thats just a guess. I will move your post to the 2nd Gen Ram section.

 

+1 check abs codes

If you have 4wal (all wheels have abs) then jack up the front and check the front hubs. Also take a look at the cables going to the hub and make they're in good condition.

Are you losing any fluid? Pull the drums off, check the wheel cylinders. Check brake lines, proportioning valves, master cylinder, etc

 

last time I had an ABS/brake light on was when my front hubs were shot and one of them got so hot it literally melted the abs sensor...my truck will never see mud again after that repair bill (i did repairs myself but how many parts it needed cost over $2000)