Low Brake Fluid warning ?!?

Last week I changed the master cylinder on my 1991 98 TS. There's still a touch of air somewhere in one of the lines, but that doesn't concern me as my father-in-law, who's been a licensed mechanic the past 45 years says that'll eventually work it's way out. My concern is the Low Brake Fluid warning on the DIS. The master cylinder is full, but I'm wondering if it may have something to do with the rubber hose which carries brake fluid dowen to the ABS unit. Perhaps that unit needs to be bled separately? Any help would be appreciated as I just got the car, but don't have a manual yet. Thanks.

Tom

I am thinking that there might of been some kind of low fluid level sensor, that you might have disconected and might have to reconnect it. Look around it and see if there is anything you might of over looked. Also you might just want to finish bleeding out the air completely out of the system to be sure that it isn't a problem. You can also try to reset the cars computer, and see what happends.

Finally got to the bottom of the problem after waisting much time and brake fluid: not one, but two bad master cylinders from NAPA. Finally went to the wrecker and applied my 275lbs to the brake pedal of cars that had the same long master cylinder until a found one that didn't budge; brakes work great now!! NAPA price with my meagre discount CDN$150.00 + taxes, wrecker price CDN$15.00 + taxes. What a bargoon + didn't have to bench bleed and I now have a spare plastic resevoir in case one fatigues on me somehow!