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12V - STS-M12 24V - STS-M24
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FAA-PMA APPROVED for Certified Aircraft

Continuous Duty (Battery/Master Solenoid). Available in 12V and 24V. Activation: -(Ground) to S-Terminal. (Floating ground frame).

All stock meets Service Bulletin 72.


  • Silver Contacts provide 300A in-rush & 150A continuous-duty capability Much higher than OE units
  • Light spring and low-current coil for excellent engagement and holding capability
  • Single coil terminal (other end of coil connected to Battery terminal)


  • FAA-PMA Certified - stop using automotive parts and operating in the 'gray area' (aka. non-conformance) of the FAR's!
  • Lamar has retooled & upgraded the GOOD, "old-school" aircraft solenoids!
  • High Quality Manufacturing designed to take the beating our piston aircraft dish out
  • Upgraded to perform best with today's lightweight, high torque starters
  • Not automotive store parts with extra mystery terminals
  • Same OE terminal layout used for decades on our aircraft - simple to install
  • Silver contacts (vs. copper) for high-current capability and long-life
  • All-metal case construction
  • Customers Also Viewed
  • Frequently Purchased With


so far so good

Richard J
March 15, 2020

Good fit. Solid construction. No more jiggling battery leads to get relay to engage.

Steven A
February 19, 2020

to replace an original equipment solenoid in my OLD Mooney, this is the only game in town (and at a reasonable price too). it fit just fine and operates exactly as expected. as usual, no complaints with anything from Aircraft Spruce.

T. D
March 7, 2019

Just Fine

February 3, 2019

This product fit in the mount and to this point accomplishes the intended task at a fraction of the OEM part.

July 20, 2018

Good Part- standard replacement.

May 14, 2020

We installed them on 3 of the Cessnas in our rental fleet. Had problems with one of them dropping out in flight. Complied with the service bulletin and Hartzell sent 3 new units. One of the new units in a Cessna 150 failed ON after about 60 hrs. We were able to bring a flat battery back. Hartzell replaced the unit for free. The replacement unit has now also failed ON after 45 hrs.

Cas L
September 12, 2018

Installed in my E-AB. Aircraft is yet to fly and this product failed with under 100 cycles of use. Only has been turned on to test/calibrate. Solenoid actuates but the contacts internally have glazed and it does not permit power to flow through. Shows 13.6 VDC in but 0.22 VDC out. Would not purchase again.

May 22, 2019


Q: What is the total current draw of the solenoid when actuated?

The total current draw is 0.8 amps.

Q: What is the difference between STec-A12 and STec-M12 relays?

The STS-M12 is for the battery master. The STS-a12 is for Auxiliary master, like a GPU.

Q: What size are the power and coil terminals? Also what is the recommended mounting orientation? I note that the 11-03161 (White-Rogers) unit recommends Cap Down orientation.

The coil terminals are #10's and the power terminals are 5/16ths. It is recommended to mount per the airframe specifications. If none, it is recommended to mount with the cap up.

Q: Does this Lamar solenoid include the diode? If not do I need it and what part number would it be?

Per Vendor: This product does not include the diode. You do not need the diode for the part to work correctly, it is simply a safety precaution some like to take. The airframe manufacturer might have a diode they recommend.

Q: What is the warranty for this unit?

12 mo from date of installation of product or 500 hrs - whichever comes first. Log books are required for warranty

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