Rear Wiper Fuse blowing - Zafria 04

[etaf]

my 04 plate vauxhall zafria is blowing rear wiper fuses (20A) from the manual thats all thats on the circuit

When you put the fuse in the wiper all works fine and then sometime later it stops working and the fuse is blown.

been suggested it may be a cable problem

any suggestions welcome please.