[RustyPile]

The white wire completes the ground side of the circuit. The reason you have 12 volts on the white wire is because apparently you have lost the ground.. The orange wire is the feed wire. the voltage is fed to the dome light through the orange wire.. Power goes through the load (the dome light bulb) into the white wire. Grounding the white wire completes the circuit and the dome light comes on. With no door jamb switches, the circuit depends on the headlight switch to provide the ground, not the turn signal switch. The only way to turn on the dome light is by rotating the headlight switch knob counter clockwise until it stops. If this doesn't turn on the dome light, look for a break in the white wire, white wire disconnected from the headlight switch, loss of grounding on the headlight switch, or other loose or bad connection in the white wire circuit.