Onan 5000 oil pressure switch

I'm chasing a no-start problem on an Onan 5000 genset. I've got another thread on that, but I have one specific question.

Is the oil pressure switch normally open or normally closed. That is, does it ground the ignition if there is no oil pressure (normally closed) or does it complete a circuit when there is oil pressure (normally open).

I'm trying to figure out if just taking the one lead off is a good way to check it or if I need to take the lead off and ground the lead.

Thanks