windshield wipers being wierd

we recently purchased an exceptional '91 classic from a major rovers north fan and are slowly getting to know all the little personality quirks. we already have our first snow and the next day the wipers suddenly wouldnt work. this was accompanied by a brief screaching noise. after shutting the engine off and restarting they just as suddenly came back on. this has happened twice. they were not frozen or blocked by snow. no other electrical seems to be affected. the alternator is an '03 delphi.

any insight would be appreciated.

thanks, gG