TOPIC: 1973 Crestliner Nordic tri-hull

I am trying to figure out what kind of stern light orginally was on this boat. The base and collar are on the boat. Was it a pole light with wires sticking out the end or is there some other part??

I think you hit it right on the head, MrMitch. It looks to me like one of the collapsible stern lights, somebody pulled the "pole" out and left the base.

What does a collapsable light look like? Did it have a socket or just wires coming out the end?

I guess they're called "telescopic" more so than collapsible, here's an example of one below. You can loosen the nut and push the pole down when it's not in use, it would have two wires coming out of the bottom of the pole;
www.wholesalemarine.com/p/ATT-7101A7/Attwood+Telescopic+Navigation+Boat+Stern+Light+with+Base.html
On the "removable" kind you pull the pole out of the socket and close the cover, the pole would have two plug receptacles for the wiring connections. The socket assy. would have the two wires to hook into the power supply there. If you look down into the socket, can you see two prongs sticking up?

When I look down through the base, I can look right throught the hole. There is no socket. Can you get the pole without the base?

Not that I know of, you could probably buy one complete and just use the pole. I believe most had the same diameter pole, but not sure. Frog has a couple for sale in the Glassifieds here, if you're looking for a period correct piece;
www.fiberglassics.com/index.php?option=com_adsmanager&view=details&id=2213&catid=4&Itemid=56