1988 300e diagnostics

I am going to try and do the onboard test tonight with my multimeter. DO I just stick the postive lead in the #3 hole on the lamda control and ground the black? With the multimeter set to duty cycle I just turn the key to one but not start the car? Is that about right or am I way here? ALso am I looking for 30% or 50%

I read the walk through in the DIY section just wanted to make sure.

Thanks

Jimmy
1988 300e
130,000 miles