Cigarette Lighter: Description and Operation
With the Ignition Switch in ACC or RUN, voltage is present at a cotact inside the Instrument Panel Cigar Lighter socket, through the CIGAR Fuse. The Instrument Panel Cigar Lighter socket shell is grounded at all times.
Whenever the Cigar Lighter is in its socket, one end of the Cigar Lighter coil touches the socket shell and is grounded. Pushing the Cigar Lighter into the socket causes the other end of the cigar Lighter coil to touch the "hot" contact. Current flows through the CIGAR Fuse and the Cigar Lighter coil to ground, causing the coil to heat up.