lcurle

masically you would be attaching a small magnet (very small) on the end of the speed needle, and a pickup under the 140 mark. Then the initial magnet "opens" the connection on the first pass, the actuator is active and the head comes out. When it passes a second time, 'Closed" the head goes back in.

An aftermarket cruis control can help with this as well if you want to go that route. You can attach a set of magnets 180 degrees from each other on the wheel, and a pickup about 3/8" away from them to measure speed as well and use the cruise as the brain for triggering the alien.