One way to test the disconnect relay, is to disconnect the wires from the small posts. Keep track of what color went where. Use a two wire jumper or two pieces of wire. Connect them to a battery source. Momentarily touch the small posts. this should activate the relay. test for continuity on large terminals. Then reverse the two wires. touch to small terminals. This should activate the real in the opposite direction. test the large terminals.
The switch should be momentary, it should have six terminals. the two outer posts on each end should have a criss-cross jumper with 12 volts DC connected to one end set. The center two terminals should be connected to small terminals on the relay.