Electronical Components

Lamar Technologies, LLC

.  (360) 651-8869
14900  40th Avenue NE, Marysville, WA 98271




We try to anticipate questions you might have about our Contactors and provide the answers here. If you need additional information send email to support@lamartech.com or call 360-651-8869


What is the difference between a 3 post contactor and a 4 post contactor?

The 3 post contactor has either an internal ground or internal power connection where as the 4 post is controlled by external ground and external power   

.   look inside?   look inside?


What is a continuous duty contactor?

A continuous duty contactor is designed to be used when it is required to be on for extended periods of time such as a Battery Master or Auxillary ground power


What is an intermittent duty contactor?

An ittermittent duty contactor is designed to be used for high current low duration use such as engine starters.


Can I use an intermittent duty contactor inplace of a continuous duty contactor?

No it could fail very quickly. Because the intermittent duty contactor is designed for higher currents the coil in it requires higher current which in turn creates more heat than a continuous duty contactor


Can Install my contactors upside down?

We recommend installing per the airframe manufacturers recommendations. In the case of a kit built or non certified aircraft it can be installed in any position desired.


I have noticed that my battery master contactor gets very warm, is that normal?

Yes generally speaking they will get warmer than would be normally comfortable to hold in your hand.


Are contactors waterproof?

No. We suggest you ensure they are protected from any moisture source.


How can I tell if I need to replace the contactor?

You can measure the voltage drop across the input and output terminals under load. If the drop is .2 volts or higher it should be replaced. Example: if the voltage in is 12.5 VDC and the output is 12.3 VDC there is a .2 VDC drop and the contactor should be replaced.


The contactor I took off only has 3 posts and the one I am putting on has 4. How do I connect it?

First you need to determin if the switch wire is power or ground. Once that is done see diagram below. Refer to question 1 for more detail.

Note: most battery master relays are negative turn on meaning the switch is acting as the ground for the contactor and most starter contactors are positive turn on meaning the switch provides power.

Click here for install instructions



Is torque on the connections important?

Yes very! DO NOT OVER TIGHTEN!!You should always use a back up wrench when tightening. If over tightened you will misalign the main studs and possibly break the coil connections on the coil studs. LOOK INSIDE click here