It's hard to say. It uses a pretty standard vintage design almost identical to many others. I had one in a collection with a similar reddish brown bobbin base, and don't think I ever did find out what it was.
Looks like this one used to have a metal baseplate that's since been removed. See that tail on the ground lead? That would normally be soldered to a baseplate, and there's no reason for it to be there if not.
edit: I just noticed the braided shield wire, which is goofy on a Fender-style pickup. The shield tends to get crammed up against the switch and ground things out on you. Makes me wonder if it was a retrofit.