Sierra MP39350 Momentary Push Button Switch 10A 12V

The Sierra MP39350 is a momentary push button switch built for the kind of jobs where you want power only for as long as your thumb is on the button. Press it and the circuit's live. Let go and it's off. That's the whole idea behind a momentary switch, and it's exactly what you want for a horn, a trim pump, an anchor windlass, a spotlight, or any signal circuit where a latching toggle would be the wrong call.

We've wired a lot of these into helms over the years, and the appeal is simple. It's rated for 10 amps at 12 volts DC, which covers the vast majority of momentary accessory loads on a typical boat. The body is brass, so it holds up to the salt air and damp that eats cheaper pot-metal switches alive. And it ships with a weather-resistant plasticized coating plus a rubber boot nut, so the face of the switch is sealed against spray, rain, and the general grime that collects around a console.

Where does a switch like this earn its keep? Think about the momentary jobs on your boat. A horn button is the classic one. You hit it, it sounds, you release, it stops. Same story with power trim and tilt on an outboard or sterndrive, where you only want the pump running while you're actually adjusting. Anchor windlass up-and-down control, a deck wash pump you thumb on for a few seconds, a spotlight you flash to signal another boat, a bilge pump manual-test button. All momentary. All a good fit for the MP39350.

The action here is normally off. With the button at rest, the circuit's open and nothing flows. Push the button and you close the circuit for as long as you hold it. Release and it springs back open. There's no latch, no detent, no on position that stays put. If you need a switch that stays on after you let go, this isn't the one, and that's by design. A momentary switch is meant to give you control only while you're actively pressing.

Construction is where a marine-grade switch separates itself from the parts-store bin. Brass resists corrosion far better than plated steel, which matters when the switch lives in a damp bilge, an open center-console dash, or a pontoon helm that sees weather. The plasticized coating over the body adds another barrier against moisture working its way in, and the rubber boot nut seals the mounting hole so water doesn't track down the shaft and into your wiring. On an open boat, that sealing is the difference between a switch that works for years and one that gets crusty and intermittent after a season.

Installation is straightforward for anyone comfortable running a couple of wires. It's a panel-mount switch, so you drill or use an existing hole in your dash or switch panel, drop the switch through, and snug it down with the boot nut. Wire it inline with the circuit you're controlling, keeping the load within the 10-amp rating. For anything that pulls more than 10 amps at 12 volts, like a big windlass or a high-draw pump, run the MP39350 to a relay or solenoid and let that carry the heavy current. That's standard practice, and it keeps the switch well within its comfort zone so it lasts.

A quick word on what this switch isn't. It's not a continuous-duty on/off switch for your nav lights or a stereo, since those need to stay on without you holding a button. It's not a high-amperage switch for direct-wiring a winch motor. And it's rated for 12-volt DC systems, so it's aimed at the standard boat electrical setup rather than household AC. Used for what it's built for, momentary DC control up to 10 amps, it's about as honest and reliable as a switch gets.

Sierra's been making marine engine and electrical parts for decades, and the MP39350 carries the same customer satisfaction warranty that backs the rest of their line. It's a genuine Sierra part, engineered to meet or exceed the original equipment it replaces, so if you're swapping out a tired horn button or adding a momentary control to a new rig, you're getting a switch that's meant to live on the water. Rig it up, seal it down, and forget about it.