Well, I'd be in there with a multimeter checking the switch for function first of all. If faulty I'd open up the casing and see if I could either fix the switch or replace it. But I'm OK with electrics.
If you go for a motor from a scrapyard it's worth checking the switch before you buy.
With the wipers in the rest position, the switch should be open.
There's no history on this forum of people reporting wiring faults, so I'd say you were really out of luck if it was the wiring loom itself. Have you had any work done around the dashboard or the rear of the engine bay recently? If so, it's possible that the wiring may have been disturbed, but pretty unlikely.