How to: Underdash lights that come on with headlights and dome light
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How to: Underdash lights that come on with headlights and dome light
I recently installed some LED strip lights under the dash on the driver’s side and passenger’s side, as well as behind the front seats, and above the cup holder (where it can't be seen). I wired it up so that in one condition, all of the lights function exactly like the dome light. They come on when the doors are unlocked with the key fob, when the doors open, fade when they're shut, come on when the thumb-wheel is rotated all the way up, and go off when it's rotated all the way down. But, I also wanted the same lights to come on whenever I had my parking lights or headlights on, and be able to dim them with the gauge cluster. I've done this on two other dodge trucks in the last week, and found some differences, but this should work on any 06-08 Ram. The switch works as a master kill switch, as well as a manual on. When in the first ON position, everything will work as designed. When in OFF position, it will completely kill power to the lights, and in the 2nd ON position, it will manually turn on the lights. This is one of my first “how-to”, so please bear with me! I’ll get pictures as soon as I can. 
Parts list.
18-24 inch LED strips, color of your choice
16 or 18 gauge wire, in red and black.
12volt SPDT (Single Pole Double Throw) five pin relay Like this
12v SPDT 3 position ON/OFF/ON Switch
12-14 gauge Insulated Round terminal end (Sorry, couldn’t find a link. It’s the connector that has a metal circle that you can put a screw or bolt through). Only need one.
Fully Insulated Female spade connectors Like this
Round barrel type splice connects for 18-22 gauge wire. Like this
16-14 gauge bullet terminals. Like this
Notes about parts
I used 4 led strips, plus one for the cup holders. Use however many you want. Eventually I will add in another one for this circuit, to light the area directly behind the center console. I have used the strips that light up from the top in two trucks, and the ones that light up from the side in one truck. I would suggest the ones that light up from the top. I bought mine from Walmart, $20 for 2.
I would suggest at least 15ft of each color wire, to make sure you have enough. Some led strips have short lead wires, so you have to make up for that.
Having fully insulated connectors is important, because the plastic keeps the metal spade from grounding out on anything and blowing fuses or creating a short, or worse. Otherwise, you need to tape the metal or wires off with vinyl tape so that the wires won't ground out.
I used the splice connects so that I could make sure I had a good connection, because I don't trust the push in quick splice connectors.
The relay must have a pin 87, and pin 87a to work properly. A 30 amp relay is fine.
The switch needs three pins: two outputs and one input. You'll connect the two power sources to the outside poles, and the leds to the middle pole. Should be rated for at least 5 amps (depending on your LEDs)
Use the insulated female spade connectors on the ends that connect to the switch or the relay, so they can just plug right in.
Tools
Socket wrench
Phillips and Flathead screwdriver
Wire cutters and crimping tool
Flashlight
Instructions
Disconnect the negative battery cable on the battery.
Mount your LEDs, and run all the wires to the driver’s side floorboard, under the carpet. I pulled the carpet back a good bit, so they would all lay down and be hidden. Twist all of the ground wires together, and crimp to the larger end of the bullet terminal. Do the same with the positive wires. You only need enough wire to get underneath the pedals (makes it a bit easier).
Remove the center bezel, the plastic panel on the driver’s side of the dash (the door must be open to get to it, use a flat head to help pop the tabs)
, and the driver’s side a pillar.
I taped and zip tied my relay to the metal frame on the opening on the side of the dash. Don’t mount it yet, but this is where we are going to put it. If you chose to put it in a different location, you’ll need to run all of your wires there, instead of out of the side of the dash.
Find a place and mount your switch, but don’t screw it in. Run one wire from the switch and out of the side of the dash on the driver’s side. Give yourself about 6 inches. One end will connect to the switch on the outside pin, the other end connects to pin 30 on the relay. Hook up another red wire from the switch for the accessory pin, and run it to the positive wires under the carpet, and crimp it. Run a black wire from your LED ground wires under the carpet up the dash and out of the hole on the side of the dash. Give yourself about six extra inches for room to play with. Strip the end about a half inch. Do not put anything on this end yet. Run a black wire from the ground on the switch, out of the opening on the side of the dash. Strip about a half inch. Do not put anything on this end yet. Connect about a 6 inch piece of black wire to coil 86. Strip the other end about a half inch. Take all three of your black wires, twist them together, and crimp them into the round end terminal. There’s a piece of plastic screwed into the frame at the top here on the side of the dash. Unscrew that screw, pull the plastic back a bit, slide your connector over the hole, and tighten the screw back. This should give you a good protected ground.
Look in your center bezel for a black plug with two wires, a white and a black wire (If you do not have this, you'll have to do an extra step, by also removing the passenger side a pillar). This wire will go to the coil, or pin 85 on the relay. If you have the plug, run three red wires (if you don't, run two) from the center bezel, under the dash, and to the opening on the side of the dash where you pulled the panel off. Leave about 6 inches hanging out from each side. Label one of these wires on both sides (DIM), and label a second one on each side (SWITCH). Labeling will help you remember what each one is.
Cut the white wire on the black plug in two, and splice it with the (coil) wire you just ran. If you haven't already labeled, do it, or connect to the relay, so you don't get the wires mixed up.
If you have the black plug with only the white and black wire in the center bezel, skip this step. Otherwise, you’ll need to remove the passenger A pillar. There should be a black plug here with nothing attached to it, it’s for cab lights. Splice into the white wire, and run it down and through the dash and out of the hole where the other wires are, put an insulated female spade connector on it. This is for the coil, pin 86.
Find the black plug with an orange wire with a blue tracer on the left side of the bezel (Sometimes stuck into a hole in the plastic).
This also goes to those who have 4x4. Cut this wire, splice in the other red wire, and crimp it back together. Mark this wire. This will go to pin 87 on the relay. On the ends hanging out of the driver's side dash, strip and attach female spade connectors.
Splice into your power point wire or your cigarette lighter, depending on whether or not you want the manual ON function to work all the time, or only when the truck is running. Run this wire through the dash to the switch, and hook it up to the other outside pin on the switch.
On the A pillar, there is a Yellow wire with a Light Blue tracer. It’s on both sides of the harness connector. Using the barrel splice connects, splice a wire to this, and run it into the dash, and back out of the hole on the side of the dash. Put a piece of tape or marking on this to remember what it is. This is for the dome light, and goes to pin 87a. Put a female spade connector on the end of this.
You should have everything connected now. Hook up your negative battery cable, get in the truck, and check out your lights! If something doesn’t work, retrace your steps, and make sure everything has a good connection, and is hooked up to the right spot on the relay and switch. Make sure your switch is on.
Parts list.
18-24 inch LED strips, color of your choice
16 or 18 gauge wire, in red and black.
12volt SPDT (Single Pole Double Throw) five pin relay Like this
12v SPDT 3 position ON/OFF/ON Switch
12-14 gauge Insulated Round terminal end (Sorry, couldn’t find a link. It’s the connector that has a metal circle that you can put a screw or bolt through). Only need one.
Fully Insulated Female spade connectors Like this
Round barrel type splice connects for 18-22 gauge wire. Like this
16-14 gauge bullet terminals. Like this
Notes about parts
I used 4 led strips, plus one for the cup holders. Use however many you want. Eventually I will add in another one for this circuit, to light the area directly behind the center console. I have used the strips that light up from the top in two trucks, and the ones that light up from the side in one truck. I would suggest the ones that light up from the top. I bought mine from Walmart, $20 for 2.
I would suggest at least 15ft of each color wire, to make sure you have enough. Some led strips have short lead wires, so you have to make up for that.
Having fully insulated connectors is important, because the plastic keeps the metal spade from grounding out on anything and blowing fuses or creating a short, or worse. Otherwise, you need to tape the metal or wires off with vinyl tape so that the wires won't ground out.
I used the splice connects so that I could make sure I had a good connection, because I don't trust the push in quick splice connectors.
The relay must have a pin 87, and pin 87a to work properly. A 30 amp relay is fine.
The switch needs three pins: two outputs and one input. You'll connect the two power sources to the outside poles, and the leds to the middle pole. Should be rated for at least 5 amps (depending on your LEDs)
Use the insulated female spade connectors on the ends that connect to the switch or the relay, so they can just plug right in.
Tools
Socket wrench
Phillips and Flathead screwdriver
Wire cutters and crimping tool
Flashlight
Instructions
Disconnect the negative battery cable on the battery.
Mount your LEDs, and run all the wires to the driver’s side floorboard, under the carpet. I pulled the carpet back a good bit, so they would all lay down and be hidden. Twist all of the ground wires together, and crimp to the larger end of the bullet terminal. Do the same with the positive wires. You only need enough wire to get underneath the pedals (makes it a bit easier).
Remove the center bezel, the plastic panel on the driver’s side of the dash (the door must be open to get to it, use a flat head to help pop the tabs)
, and the driver’s side a pillar. I taped and zip tied my relay to the metal frame on the opening on the side of the dash. Don’t mount it yet, but this is where we are going to put it. If you chose to put it in a different location, you’ll need to run all of your wires there, instead of out of the side of the dash.
Find a place and mount your switch, but don’t screw it in. Run one wire from the switch and out of the side of the dash on the driver’s side. Give yourself about 6 inches. One end will connect to the switch on the outside pin, the other end connects to pin 30 on the relay. Hook up another red wire from the switch for the accessory pin, and run it to the positive wires under the carpet, and crimp it. Run a black wire from your LED ground wires under the carpet up the dash and out of the hole on the side of the dash. Give yourself about six extra inches for room to play with. Strip the end about a half inch. Do not put anything on this end yet. Run a black wire from the ground on the switch, out of the opening on the side of the dash. Strip about a half inch. Do not put anything on this end yet. Connect about a 6 inch piece of black wire to coil 86. Strip the other end about a half inch. Take all three of your black wires, twist them together, and crimp them into the round end terminal. There’s a piece of plastic screwed into the frame at the top here on the side of the dash. Unscrew that screw, pull the plastic back a bit, slide your connector over the hole, and tighten the screw back. This should give you a good protected ground.
Look in your center bezel for a black plug with two wires, a white and a black wire (If you do not have this, you'll have to do an extra step, by also removing the passenger side a pillar). This wire will go to the coil, or pin 85 on the relay. If you have the plug, run three red wires (if you don't, run two) from the center bezel, under the dash, and to the opening on the side of the dash where you pulled the panel off. Leave about 6 inches hanging out from each side. Label one of these wires on both sides (DIM), and label a second one on each side (SWITCH). Labeling will help you remember what each one is.
Cut the white wire on the black plug in two, and splice it with the (coil) wire you just ran. If you haven't already labeled, do it, or connect to the relay, so you don't get the wires mixed up.
If you have the black plug with only the white and black wire in the center bezel, skip this step. Otherwise, you’ll need to remove the passenger A pillar. There should be a black plug here with nothing attached to it, it’s for cab lights. Splice into the white wire, and run it down and through the dash and out of the hole where the other wires are, put an insulated female spade connector on it. This is for the coil, pin 86.
Find the black plug with an orange wire with a blue tracer on the left side of the bezel (Sometimes stuck into a hole in the plastic).
This also goes to those who have 4x4. Cut this wire, splice in the other red wire, and crimp it back together. Mark this wire. This will go to pin 87 on the relay. On the ends hanging out of the driver's side dash, strip and attach female spade connectors. Splice into your power point wire or your cigarette lighter, depending on whether or not you want the manual ON function to work all the time, or only when the truck is running. Run this wire through the dash to the switch, and hook it up to the other outside pin on the switch.
On the A pillar, there is a Yellow wire with a Light Blue tracer. It’s on both sides of the harness connector. Using the barrel splice connects, splice a wire to this, and run it into the dash, and back out of the hole on the side of the dash. Put a piece of tape or marking on this to remember what it is. This is for the dome light, and goes to pin 87a. Put a female spade connector on the end of this.
You should have everything connected now. Hook up your negative battery cable, get in the truck, and check out your lights! If something doesn’t work, retrace your steps, and make sure everything has a good connection, and is hooked up to the right spot on the relay and switch. Make sure your switch is on.
Last edited by JoshuaAckley; Feb 20, 2013 at 05:29 PM.
