I went back and read all your stuff again, and I have two notes. One, the relay has no continuity. Two, the fusible link was blown. Did the relay internally short and burn up the relay, or did another short shunt enough 12v into the relay coil to fry it, and on the way, finally pop the fusible link, which will last a while under a mild current excess - designed that way, which is why you use both fuses and fusible links to protect systems of varying vulnerability to overcurrent.

Not responsible for advice not taken...