Definitely have a short and I recommend looking at the wiring diagrams on this forum and track down the short. Always look at anyplace splices have been made, places your wires go through sharp holes and around linkages, and look for any overloads on the system. Good chance it might be a short to ground someplace if the fuse blows quickly every time. The fuse blows to prevent a fire or other more serious damage. You are correct that a relay could also cause the fuse to blow.
The wiring diagram will provide a good start!