1991 Toyota Corrolla electrical problem

1991 Toyota Corrolla, 1.6 engine, 180,000 miles, air, auto.

The "brake" and "batt" lights illuminate intermittantly together, dim and bright. Sometimes they flash on and off. Car starts great, had the alternator checked on a machine at my local parts dealer, checked good. Battery voltage checks good and is being charged with engine running. Running down the road, the lights come on and off. Everything appears to be working ok. Both of these lights come on at the same time, when driving down the road.