I have a faulty rear wiper relay on an impreza, but I cannot identify it's part number.
It's 12v, but what Amperage?
It has a part number and details as follows
- NILES JAPAN
It has 5 pins.
Do you mean you're unsure whether the part number is 12V5B-1T or 642N? Odds are good it is one of those. Try searching for each (e.g., feed "12V5B-1T relay" to the Google) and see what you get. It is very likely you'll get specs with a picture.
By the way, it is probably not a 5-pole (five switched circuits) but rather 5-pin or five connectors or some such. A relay will usually have 2 connections for the coil (to operate the relay), at least one common connection for the load, and then one connection for each pole. So a 5-pole relay would have at least seven connections, and more likely eight (or more).