'95 88 Olds Brake Light on after Master Cyclinder Change

Hi all,
Had to replace the rear wheel cylinders on 2 of my olds 88's (1995 & 1999). Bled the brakes on both. The 99 has no problems.
The pedal in the 95 kept going down as if there was air in the lines.
Bled the brakes again but still the same thing. Was told by my mechanic
that the master cylinder was bad so I replaced it with a new one.
Immediately after replacing it the brake light came on and the dinger kept chiming. He said apparently the float was stuck in the new one and we unplugged the harness on the master cyclinder and drove a few days to see if the float would unstick.
The float didn't unstick so I exchanged the master cylinder with another new one. Same thing happens. I bench bled the master cylinder then bled the lines at the master cyclinder so I don't believe there is any air in there. This car does have ABS but I don't think there was anything else I should have done.
Any suggestions?
thank you!

You may have air in the abs unit you need a scanner equipped to actuate the abs solenoids to bleed the abs.