If you've got a soldering iron, you can take the cover off of the main relay and resolder all of the joints. These relays typically fail because of a cold (sometimes called dry) joint which means that there is a crack in the solder. The relays are over $50 new and you can resolder one in about 5-10 minutes.

Before you get out the soldering iron, however, you can test the relay using the procedures outlined in the service manual. It involves applying 12V power to specified connection tabs and checking for continuity between others as the relays are activated.