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How To: Install Underdash Lights


New Member
Apr 3, 2009
Reaction score
Mount Vernon, IN
Vehicle Year
1989, 2001
Make / Model
Engine Size
2.3L 4-Cylinder, 2.5L 4-Cylinder
I recently decided to add more lights to the interior of my 89 Ranger, taking an idea used on F-150's I incorporated it into my ranger, this is how I did it.

1. Find some light sockets out of a donor vehicle, any Ford Truck will work, or car for that matter, I got mine out of an 86 Mercury Grand Marquis, make sure you get the power wire that goes with the socket and any bolts.

2. Make sure you have some wire the same gauge as the power wire (14/16 GA) Color doesnt matter, I used Red for my power wire, and Black for a Ground, Look under the dash to find an open hole to mount the socket, make sure that the socket mounts as far up as possible to keep it from getting kicked by passengers or drivers.

3. Open the passenger door and locate the interior light switch and remove it from the door jamb, notice the color of the wires coming out of the switch, locate these wires on a wiring diagram and tap into the wire for the on/off function, this wire will run from the door jamb switch on both sides and to the headlight switch and the dome light, the other wire (the one you dont want) runs power to the headlight switch and goes to fuse; because the switch will supply power to the light, you only need to tap the one wire, make sure to attach enough wire to connect to your power lead you obtained from the socket, connect the power wire from the switch to the wire from the socket using a butt connector, tape up all wires and re-install the door switch.

4. Ok you have the socket mounted, power supplied, but no light? Thats because on most Rangers, an auxillary ground wire needs to be ran to supply the completed circuit. To Install a ground wire, find a bolt that attaches to the body or a wire that grounds another item, on my lights, I grounded it to the bolt that grounds the PCM behind the passenger kick panel, as long as you dont create a spark to the PCM or unground it completely you will be fine. Attach your ground wire using ring connectors to your mounting screw and secure, test your light by opening each door individually and then with the door closed, turn on the dome light with the headlight switch..if your floor lights up then we can install the driver side light.

5. To Install the driver side light, do the same as you did for the passenger side, with one slight difference, using the power wire from the passenger side, run a power lead from this wire to your other lead wire, the reason for this is because the driver side door jamb switch is set up differently and theres not enough wire or a place inside the body to run the wire for concealment, so its easiest to run it off the passenger side. Conceal this wire by running it above the ducts for the heater floor vents and connect as before using a butt connector.

NOTE: If you grounded the other light to the metal frame that runs along the bottom of the dashboard, then no ground wire should be required, if you did not do this, then you will need to run a ground wire from a ground point on the driver side floor (good spot is the brake release assembly), make sure you conceal your wires to prevent damage. Secure all wires and screws and test as noted in #4 above.

Thats how you install underdash lights in your Ranger.

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