It's the relay you hear when you turn the ignition key. It's job is to direct all the power from the accessory circuits to the ignition to prevent the system from being overloaded. I am hedging my bets now and will say your ignition problem is revolving around the fuel cut solenoid on the carb. Disconnect it and try to start the engine (will require a few stabs on the throttle to prime the throats as the solenoid won't let it pull fuel up). If it coughs and shows some sign of life you have more than likely found the culprit.