12v reading means very little, if anything.
Open the other switch, dont disconnect anything, but tell us what you have.
Photo of both would be great - if you dont know how to post a photo, ask![Wink ;) ;)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
Open the other switch, dont disconnect anything, but tell us what you have.
Photo of both would be great - if you dont know how to post a photo, ask