Going by memory but a hot wire is on the pin on the center of the socket and the socket either grounds through the metal dash or there may be a ground wire on a tab on the socket. If one were to run two lighters i would think you could splice off the hot wire of the existing lighter. The ground is easy either through the metal dash or a dedicated ground wire. i also beleive the wiring may already be there if the factory ran two lighters etc.