Posted for <donaldgordon@bellsouth.net>:

 I'm connecting a VEP pressure switch (part # 654A53) to my pitot/static
 system for a gear warning device.  I purchased the device from Lancair
 marketed as a safety squat switch.  The device has 3 wires from the switch,
 white, blue, and red.  The device did not come with a wiring diagram.  If
 someone has wired this device into your aircraft, could you identify the
 purpose of each of these three color-code wires?  BTW, the Lancair manual
 indicates the white wire is not used for standard installations (leaving the
 red and blue wires).  My gear warning circuit will require the switch to
 close when the airspeed is above 90 mph in order to complete the ground that
 powers the warning light.
 
 Additionally, does anyone know if you turn the adjusting screw clockwise or
 counterclockwise to decrease the speed at which the switch will activate?
  
 Don Gordon
 Orlando, FL
 LNC2

[Hi Don, You'll probably get the answer to which wires are which before you can go through this little test, but for future reference here's how you determine which wire (or terminal) does what.  A switch with 3 terminations is generally known as a SPDT siwtch, for Single Pole Double Throw.  One of the terminations is common (C), and the other two go to the movable contacts. When the switch is in its resting state (ie, not actuated or thrown) you'll find a short circuit (zero ohms) between the common and the normally closed (NC) terminals.  When the switch is actuated you'll find the short between the C and normally open (NO) terminals.  (In your case just think of the wires hanging out of the switch as the terminals)  When you've got a switch that has no labels the test goes something like this.  Leave the switch at rest, not thrown, and find the 2 terminals that are shorted together (zero ohms on your ohm-meter).  When you do you will have identified the remaining terminal as going to the NO contact.  Take one of your ohm-meter leads and connect it to that NO terminal.  Throw or actuate the switch and find out which of the original 2 terminals is now shorted to the NO terminal you're already hooked up to... of those original two the one that shows you zero ohms is the common (C).   Now all you need to do is determine how your circuit operates, choose the correct switch operation (shorted when actuated or shorted at rest) and hook it up.  Trust me, the actual testing part goes faster than reading about it <g>.  I hope this helps.  <Marv>  ]