TSP-12 and TSP-24 transient spike protectors add system safety by ensuring an exit to ground, should an AC or DC spike invade the vessels charging system. Fused diodes are designed to fail before alternator diodes are likely to be damaged. A common electrical disaster can happen when the ignition or battery switch is turned OFF and thea alternator is ON, resulting in damaged alternator diodes and lost ability to charge your batteries. The TSP sacrificies itself to save other expensive components. Mounts directly to the alternator between positive & negative contacts.