Cooling fan relays

Are you sure you are replacing it with the right one? It will melt from too much amperage flowing through it, probably your fan is drawing too much power from a drag somehow

There two things that's going to melt a relay. One is bad/loose/dirty electrical connections. They cause a resistance and current through a resistor causes heat. The second cause is the same deal on the contacts inside the relay. -- When your relays melted, was it on the contacts going in or was it internal? If it was internal melting, the relay is too small or the fans are drawing too much current. -- The fans are almost thirty years old and the bushings may be dry. I doubt that they have a current rating on the label but if they did you could check how much current they draw.

Electrical wires get old and brittle just as we do with age. Heat is the main source and they will short out or create too much resistance and heat up and burn out. Also the fan bearings may wear out, creating a drag on the fan, causi9ng the motor to overwork, drawing too much electrical current, causing excessive heat, melting the wires. This happened to my corvette. I just put in new fans and had an inline fuse put in to protect the wires from over heating. Make sure it is a good made fan, not a cheap china one, and it is strong enough for your car.