So I've got a nice new standard (non-ABS) master cylinder for a Sierra. I know that the two connections on the side go to the front and rear braking circuits but there's also a connection at the far end (as viewed by the driver) on the underside. Does anyone know what this is for?
Thanks Alex

the two front ones go to the front brakes, and the rear one goes to the back, then splits with a t piece.

There should be 2 connections for the split circuit front brakes [one to each caliper] and one for the single circuit rear.

Stu

Thanks - makes sense now.