The dome light uses two wires as well, to an insulated socket without a ground which has a 2-contact bulb, also not grounded. Both wires go down the windshield A pillar and under the dash, one to ground at either a door switch or the dimmer switch of the dash light circuit at the headlight switch. The other lead to the dome light goes directly to the fuse block and is hot all the time. Use about a 5 amp fuse to that circuit.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!