Brake light/ABS light on

[Lordsman]

Red brake light accompanied by yellow ABS light came on on the dash.
Any ideas what the problem could be? One suggestion I've heard was the ABS module needed to be rebuilt, but I've never heard of that. Is there a sensor above the rear differential like there was on 2nd gens?
Truck is a 2005 Cummins 3500.
Thanks in advance!

 

[Lordsman]

I moved this over to non engine/transmission section. Thx

 

[Mark 5.9 coalburner]

In my 05 it wound up being my front wheel bearing. You have sensors on both wheels. The sensors are plugged into the back of each hub.