The dome light and light harness is a separate item. I've never seen a truck with no dome light at all, so I'm not sure how much of the wiring is already in your truck.
This is how my factory setup works.
- Orange and white wires for interior lights come from under dash near the emergency brake, and then run down under the door kickplate and up into the cab corner behind the seat. These wires are also connected to the door switches (white wire only) and the factory under-dash courtesy light.
- Orange wire always has power, and the white wire is grounded to activate the interior lights (both dome and under-dash lights). White wire is grounded by one of the door switches, or by turning the headlight switch full counter-clockwise.
- In my truck there are push connectors where the two wires come up into the cab corner, and the dome light and exterior bed light are plugged into those wires. Factory setup is designed so that the exterior light will only switch on if the interior lights are also on.
- Dome light wires run up the cab corner and into the space between the two cab layers, and then across to the dome light. Its a short distance, and fairly easy to snake the wire across.
Do you already have door switches and/or an under-dash courtesy light? If that wiring is in place it should be fairly easy to install the dome light.
I don't know if newer dome lights are the same, but mine has the light socket set up to be electrically "floating" or insulated from the housing with small spacers. That allows them to provide constant power to the light and then switch the ground.
LMC truck sells a dome light wire harness, but I can't tell how long it is.
Bruce