I recall at one point I had the button connected to the fuel pump circuit, to fill the float bowls. In the original hookup, the electric pump was tied in with the oil pressure and starter circuit for safety in a crash. After the fuel eveporates from the float bowls, some time cranking the engine is needed to fill the carbs with fuel. What I have now is a modified relay, the one with a red mark. It turns the fuel pump on with the ignition switch which is more convenient than going in back an pressing the button to fill the float bowls. Though not as safe in a crash.