I would test the 2 large contacts on top of the start solenoid with an ohmmeter without power applied. If they are shorted or show a resistance then the solenoid is bad. If that shows an open circuit, Then without power applied test the start button and the wires that connect it to the MPEM to see if that is shorted out. If that is ok then disconnect the control input at the base of the start solenoid (probably a white wire) to see if the MPEM is constantly energizing the solenoid