ABS light on == ABS codes stored. You'll need a high feature scan tool to access the ABS control module to read the codes, but that is definitely the place to start.

 

The truck will store previous codes even if they are intermittent & the CEL (Check Engine Light) isn't on at the time you have it scanned.
ABS is freaky & really annoying when it clicks on (kinda makes you panic lol), but if it were so wrong then I don't see why (I believe) it's mandatory on all general passenger vehicles since who knows when?

 

abs will store a hard code, know your facts before trying to help and u will need a scan tool that will read abs, i own a nemysis and a genysys and have had this issue check for ground under the washer bottle