Wiper circuit blows fuse

I had a problem recently with my wipers not working. The fuse was blown and I replaced it but the new one blew immediately when I switched the wipers on. There was a 25 amp fuse in the fuse box so I replaced it with a 30 amp (hopefully temporarily) and it seems to be working now. I really don't want to overload the circuit. Can anyone tell me if a 25 amp or a 30 amp fuse belongs in the wiper circuit and where should I look first to find what is blowing the fuse??