p'up replacement

What are the old and new pickups (manufacturer, model?) What's the rest of your setup?

Guessing a bit: if it's got four wires the new one is almost certainly a humbucker. So I'd guess it's replacing a humbucker with only two wires (the original one for the guitar maybe). A four wire humbucker gives you the ends of both coils, the two wire one will have them connected end-to-end inside the pickup somewhere. Usually the manufacturer will have a sheet telling you the colour codes and which two wires need to be connected together, they might already be soldered together.