Try www.pdftown.com for a car manual that will have wiring diagrams in it.

Try Google or other search engines on the net

Go to samsung website. Check support tab and dowload manuals in pdf form. Most manufacturers support older products for  a while.

Some time they dont fit drain plug. You should warm the motor up for seveal minute then stop enine and tip mower upside down and allow  used oil to run out of the filler/dipstick tube. When all the oil is out tip back over and fill up with new oil to the correct level. I dont know this model but some have an oil filter that also needs to be changed. My Victa with a honda motor uses tis technique.