It's an '01 Ram 2500, four wheel discs. While driving yesterday the ABS light came on, didn't overly concern me. But a few minutes later the regular BRAKE light came on as well. I did a visual & didn't find anything wrong, the braking effort thus far doesn't seem to have degraded any. I tried disconnecting the battery to see if maybe it had just been an electrical glitch & they might re-set but that didn't change anything. Could the master cylinder be bad & only either the front or rears are working? Being disc, maybe they just seem to be grabbing as normal? My jackstands are currently in use so I can't raise it up yet to see whether all four are grabbing. So I thought I'd come here to see what anyone can tell me. I'm currently unemployed so I can't afford to take it to a shop for a diagnosis. Thanks.

did you check the fluid level? Not just look on the outside, as sometimes a line gets made by gunk and it looks higher than it is.

I would replace the brake fluid before taking anything apart. Speed bleeders are available for your truck. I replace the brake fluid in all my cars/truck every 2-3 years to keep rust from messing up the antilock controller.

Take it somewhere and have the codes read for you.
The ABS light will only come on for a ABS system issue, not a master cylinder or caliper. Don't throw parts at it and expect to fix it.

I had the same problem on my Ramcharger. When I changed the fluid it all worked fine.

For what it's worth, I used my own code reader on it, didn't show any codes. Wasn't aware that old fluid was ever an issue (never ran into that before) but at 160k that's certainly worth a shot, especially since I still don't feel any abnormalities with the brakes. I do still wonder about an electrical glitch, though, since at one point yesterday the lights were off after start-up, then came back on after the next start. Thanks.