how do i check the no1 injector resistance?

hi i need to check the number one injector resistance on a frontera 2.5td lwb 1998 we have had a diagnostic check and one of the codes says probs with no1 we have checked and cleaned but need to check the s=resistance to see if anything we have done has worked then reset the codes,,,, some diagrams would b helpful so we know where to put the metre etc

cheers kirsty