Stocks opened lower in light trade Monday, as markets looked ahead to Tuesday's presidential election. The S&P 500 and the Dow Jones industrial average dipped 0.4% each. The Nasdaq traded down 0.1%. Volume was sharply lower, down 18% on the Nasdaq and 15% lighter on the Nasdaq compared with Friday's trade. The services sector slowed in October, sending the Institute of Supply Management's services index to 54.2, down from 55.1 in September.