1997 gm b7 no abs The auxiliary brake light and alarm is coming on after the bus is driven when it comes on you can restart the bus and it stays off till you move the bus. the brakes,sterring and booster motor are working fine. After siting overnight it may not do it agen for several days. I have swapped the booster flow swich and multifunction alarm out.
If you have changed the little black box (I am assuming that is what you mean when you say multifunction alarm) then the only thing left is to check all your grounds and power connections. I have quite a bit of trouble with these and most times it is a loose ground/ power at the battery or starter. My drivers know to click the ignition switch off and on w/o even letting engine quit. Good luck