Brake problem?

90's had ABS, that's odd, before this happened my rear brakes locked up a couple times during the week under light pedal pressure so hmmm I'll check into that as well.

The master was bled as well and the first time I lost the pedal one of the lights that show all four wheels came on briefly but I don't even know what that's about. I just bought the truck a couple weeks ago and haven't sorted out the ins and outs.

Starting to suspect a bunk master cylinder, got a rebuilt one so who knows, taking that back and getting a new one, see if that helps.

Thanks for the suggestions guys