My 97 RAM 1500 4X4 has the ABS/Brake light on.
The brake hydraulics are fine and it has a new Master Cyl.
I got some advice that maybe it was the rear axle speed sensor gone bad.
I disconnected the connection for it above the rear differential and the light remains on.
How can I trick out the sensor connection to make the light go out so I am sure this is the problem? Thanx!

get the codes for the brake system. ground out the plug under the dash, by the steering column. count the flashes on the brake light. this will tell you whats making the light go on. i don't know of a way to "trick" the rear end sensor. change it out, and see what happens. they are relatively inexpensive.

A burnt out light bulb (or fuse I can't remember) caused my 96 to trigger the ABS light. Easy to check.

Sheldon

If it is a posi axle pull the cover and check to see if the clips that align the clutches has broken and damaged the sensor. Most of the time it also damages the caps that hold the carrier in place.

maybe ohm the sensor out? IIRC it has a rather high reading 1300-1600 ohms. Obviously if it's "open" it's bad.