that fuse will be hot with 12v at all times. idk if that wiring diagram is right thats posted above. it shows its a 30amp fuse but you have a 40 amp ciricled.
I would check for power at relay should have 2 termanls with 12v, if that wiring posted above is right then check it at pins 86 and 30 should have power. take paper clip jump 30 to 87 fan should come on if it doesnt then yuou have a wiring problem.
if your not getting 12 v but getting some power at fuse my guess is have high resistence in that wire not letting full power there.