Gmc 1997 c1500, 5.7l. P/u. Replaced ABS, brake lines, master cylinder, rear cylinders, rear brake pads. Have ignition in first position, pumped 3 times, held brake, bleeding back rear and getting mostly air with some liquid. Did 8 times today, no change. (Been trying for 2 days, master cylinder is primed properly) Should ignition be on, what position?