Honda Accord 98 Electrical Issues

I have a 98 Honda Accord with 180K miles. Had a recent issue with the battery, brake and all 4 door ajar lights flashing on while I am driving. This happens repreatedly. Have had the alternator replaced with an aftermarket alternator. Problem is back again although not as frequently. In addition, now the warning light for a rear brake light out is also flashing along with the others. My mechanic has searched for a possible grounding issue but has found none. I asked a local Honda service department about the issue and they suggested that the aftermarket alternator should have been replaced with a Honda alternator. Any suggestions where we should head next? Many thanks.