#2 (the bottom one) is the Number-1 Chain tensioner
#3 (top one) is the Number-2 Chain tensioner
Oil pressure switch is on the right-side of the block for the 2T engine. I'll have a check on my 18RG stuff and see where it is. I just checked my engine and it has a blank panel like yours and the car has an oil pressure gauge, so it has to be bolted onto the block somehwere.