Our replacement inline diode works with our 1514-21 circuit kit or our 1514-23 Inline Diode Kit. A Diode works in the electrical system as a one way valve. It allows current to run through it to the Voltage Regulator inside the Alternator ( "SI" series Delco's)  but does not allow current to go back through.  This eliminates engine run-on.  Sometimes the electronics inside certain Alternators will allow current back feed and return to the Ignition switch. In turn energizing the ignition side of the system and allowing the engine to continue to run after the key is shut off.  The Diode eliminates this problem. A Diode has a certain way it is installed. The arrow that is on the Diode must face or point to the Alternator. That is the correct way the Diode is installed.