Most of them were Perko. The 3 wire suggests that there are two lights--one aft and one forward. That is not necessary for most C Dorys, since an all around light works as the steaming light and stern light--however, some of that vintage boats did have a real stern light (mine was on the aft cabin house), and thus did the forward steaming light, and then both bulbs for the anchor light.
This might be a good time to switch to an all around LED anchor light/steaming light, and fi you have the aft anchor light--ditch that, or better yet, make it a cockpit light.