Lear Corp., an auto parts maker on a downsizing jag, is laying off 100 employees at its plant on Waters Avenue in Tampa. The factory produces electronic circuit cards for use in automobiles, some of the manufacturing the company has been shifting to countries with lower labor costs. Of Lear's 91,000 worldwide employees, only a fraction still work in the United States. Lear acknowledged the layoffs Tuesday on the online Florida Worker Adjustment and Retraining Notification list. Lear is a Fortune 500 company founded in 1917 in Detroit. Downsizing helped it turn a profit of $240-million last year after losses totaling $2-billion in the previous two year.