1990 Cadillac Deville

You could bench test the relays by the use of jumper wires, a meter, and a power source(battery). On the side of the relay case is a layout of the circuitry with corresponding terminal numbers. About all you can do is power the control circuit, and use an ohmmeter to verify continuity through the relay switched contacts. Is there also an overheating concern that goes along with the fans code, and have you cleared the code to see if it returns?