Sierra MP39120 Marine Ignition Starter Switch – 3-Position, Conventional, 3-Screw, 12V/15A
Free returns on all eligible orders
You have 30 days to request a return. All sale items are final sale.
Sierra MP39120 Marine Ignition Starter Switch – 3-Position Conventional, 3-Screw Terminal, 12V/15A
The Sierra MP39120 is a heavy-duty marine ignition starter switch built for conventional ignition systems with screw-terminal wiring connections. The 3-screw terminal layout is the key differentiator from blade-terminal switches in this family — screw terminals accept ring and spade lugs directly, making them the preferred choice when your wiring harness uses crimped lug connectors rather than blade-style push-on connectors.
A corrosion-resistant polyester housing with an inner cylinder seal keeps moisture out and prevents shorts in demanding marine environments. The 3-position action — Off, Ignition, and Start — provides clean, positive control over engine startup and shutdown, backed by a 30A solenoid rating and a 15A circuit rating. The 1-1/8" cylinder diameter and 7/8" mounting hole fit a wide range of marine dash panels. Note: no push-to-choke function is included.
Key Specifications
- Part Number: 11-MP39120
- Switch Type: 3-Position (Off – Ignition – Start)
- Ignition Type: Conventional
- Voltage: 12V DC
- Current Rating: 15A
- Solenoid: 30A
- Cylinder Diameter: 1-1/8"
- Mounting Hole: 7/8"
- Terminals: 3 Screw
- Housing Material: Polyester (corrosion-resistant)
- Inner Cylinder Seal: Yes
- Push-to-Choke: Not included
Compatible Applications
- Outboard and inboard engines with conventional ignition systems and screw-terminal wiring harnesses
- Marine helm panels with a 7/8" mounting hole accepting a 1-1/8" cylinder switch
- Installations using ring or spade lug connectors rather than blade-style push-on connectors
- 12V DC electrical systems requiring a 3-position Off/Ignition/Start switch
- Direct replacement for worn or damaged OEM conventional ignition switches with screw-terminal connections
Parts Desk Insights
The MP39120 is the right choice when your conventional ignition wiring harness uses ring or spade lug connectors that terminate to screw posts — a common configuration on older and custom-wired vessels. If your harness uses blade-style push-on connectors instead, the Sierra MP39770 Conventional 3-Blade Terminal Switch is the correct fit and includes a boot. For a 4-position switch with an Accessory position in the same 1-1/8" polyester format, the Sierra MP39800 4-Position Conventional Switch is the next step up. If brass construction is preferred over polyester, the Sierra MP39060 Conventional Brass Switch or the Sierra MP39080 Conventional Brass Switch are the traditional-material alternatives.
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 1-3 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
Returns & Satisfaction Guarantee
We stand firmly behind the quality of every product we sell. Your confidence matters to us — and we back it with a straightforward 30-Day Satisfaction Guarantee.
If you are not fully satisfied, you may request a return within 30 days of delivery. All returns must receive pre-approval prior to being sent back. Unauthorized returns will not be accepted.
To qualify for a return:
Item must be in new, unused condition
Product must be in its original packaging
All parts, components, hardware, manuals, and accessories must be included
Packaging must be undamaged and suitable for resale
Important:
Electronics are strictly inspected. No returns on open-box electronics. Exceptions may apply only with prior written approval. Any electronic unit that has been installed, powered, activated, or altered may not be eligible for return.
We are serious about product integrity — and equally serious about taking care of our customers. If there is ever a product issue, contact us immediately so we can make it right.
For return authorization, please contact our support team before shipping anything back.