fuse keeps blowing.

ok i have my setup and im running into problems,i put two relays because i have two compressors.well the wire that goes to the 12volt ,i have a fuse on there,(do i need one) well the fuse keeps blowing.i turn off the car and turn it back on and it blows.does anybody know what the problem is? i have two 380 compressors,with two 40 amp relays.connected to eatch comp.also does anybody know whats the deal with the akron fittings.i think thats whats there called well my line doesnt want to stay connected to them..?