1997 FORD EXPLORER seems to brake differentially - ABS light on - BUT not RED brake light?

I noticed that my right front caliper is braking & not the right caliper & this coincided with an ABS light - but no red "brake" light which would seem to indicate a bad proportioning valve, bad circuit in the master cylinder OR frozen front caliper ? Truck has 220K + miles on it .. But runs fantastic except for brake issue. This has caused me to go into a spin on the freeway when I hit my brakes also makes the truck want to change lanes when you stomp on the brake pedal - really pulls ..any ideas would be appreciated .. thanks