Brake light flashes & goes off; Rear ABS light stays on until I turn engine off and back on?

1993 Ford Aerostar V6 Extended minivan. Couple of months ago weird things started happening to brake warning lights on dash. In a.m., (cold engine), when first driving, the red brake light will flash on then off; then the yellow Rear ABS light comes on and stays on. If/when I turn engine off and restart, all goes away. Was thinking electrical problem? But, now this is happening more frequently. Example: after turning engine off and back on, the lights will do the same thing for a second time. Third time of engine off/on, lights don't do it. (Just had auto in shop for power steering pump replacement & didn't think to ask mechanic about brake lights. But, I DID ask the mechanic to check all fluid levels: brake, oil, transmission, radiator. He said all was fine with them.) My brakes work, car stops. Is it just electrical? What is the "testing" I've been reading about in the answers about ABS? Should I be concerned?