Compatible replacement for Sierra MP390601 conventional 3position marine ignition switch. Designed for Off Run Start operation and rated for 15 Amp at 12 V DC. Key benefits Direct compatibility: matches the conventional 3position layout used by Sierra MP390601 for straightforward replacement. Reliable electrical performance: rated ignition capacity of 15 Amp at 12 V DC for typical small marine engine ignition circuits. Leakproof design: helps prevent water intrusion that can cause shorts and electrical failure on the water. Rustproof components: built to resist corrosion in marine environments and extend service life. Flexible and adjustable fit: accommodates varied mounting locations and wiring arrangements to simplify installation. Function and specifications Type: 3 position conventional Switch positions: Off Run Start Rated ignition current: 15 Amp at 12 V DC Compatibility: suitable as a replacement for Sierra MP390601 conventional 3position marine ignition switches Materials and construction: corrosionresistant and leakresistant components for marine use Problem description and urgency Symptoms that indicate a failing ignition switch include no crank or intermittent starting, visible corrosion on terminals, moisture or water ingress around the switch, a loose or sticky key action, or electrical arcing when starting. These issues can leave a boat unable to start or cause further electrical damage. Urgency: immediately if the switch shows signs of corrosion, moisture ingress, or inconsistent switching to avoid being stranded on the water and to prevent potential wiring damage. If possible, document the condition with clear pictures of the switch, terminal area, and wiring before removal to confirm compatibility and for future reference. Use scenarios Routine replacement during boat maintenance when the original ignition switch shows wear, corrosion, or poor contact. Emergency dockside swap to restore starting capability after a switch failure during predeparture checks. Refitting or refurbishing small outboard or inboard control panels where a conventional 3position ignition switch is required. Installation notes Check that wiring and terminal layouts match the existing switch before installation. Clean surrounding wiring and terminal connections to ensure good electrical contact and to avoid transferring corrosion to the switch. Verify the switch rating meets the electrical load of the ignition circuit; 15 Amp at 12 V DC is suitable for standard ignition systems but confirm for higher accessory loads. This replacement switch provides a straightforward, corrosionresistant option to restore conventional Off Run Start ignition control on compatible marine engines.