In about 10 minutes of searching, i struck out on a manual for the WDS1600. Did find several references to that sander having be "made by" Steel City as a clone of the Steel City 55210, and since they are out of business thought i'd hit a dead end. Took a few minutes but i found a link straight to the 55210 manual, attached. Yours may or may not be a direct clone, but maybe this will be close enough to get you on the right track. Most of the hits i did find for the WDS1600 were folks looking for the manual, so this may be a better bet!!
Welcome to the forum, and good luck with the sander!!
earl