hi all...

im changing oil pressure switch on my z18xe vectra c , do i disconnect the battery before removing the plug for doing this...
also changing oil pressure sensor o ring seal and slightly worried about over tightening when putting back on ..and im going to change oil and filter while at it so can anyone tell me best type of oil to use and how many litres ,(4.25l)

first attempt at this sort of thing ...

thanks guys .