Welcome to IRV2
Lots of things can cause the ABS light to stay on. First off, which chassis manufacturer do you have? Call the chassis service number and ask them. It may be simple, it might not be.
There is also another resource - tiffinrvnetwork.com. They are a Tiffin owners forum with lots of experience to help you. There is also a Tiffin subforum here on Irv2.
Roger & Mary
2017 Winnebago Navion 24V (Sold)
2014 Tiffin Phaeton 36GH (Sold)