See www.surfncircuits.com for a complete description. This github repository contains the Kicad Schematic and LTSpice (tm) simulation of the timer.
KC_TrunkLightHack: Kicad schematic of the Analog Circuit
LTSims: Spice simulation file for the Circuit
Datasheeets: Datasheets for devices.
See the complete blogs entry at www.surfncircuits.com