4x4 Dash Indicator

paauto · May 24, 2018

I added an orange LED in my speedo cluster that lights up when I'm in 4WD. I tapped into the wires that feed the LED on the 2/4WD dial selector. The white wire in the factory harness is + and the brown/black wire is -. The "Transfer Case Control Module" closes the ground circuit when in 4 Hi and allows the LED on the factory dial to illuminate. I simply piggybacked off of this. I have pictures of the whole installation and will post a link to them once I have my kid show me how to do it. I also have a blue LED on the opposite side to indicate when my light bar is on (I turn it on/off with a pneumatic foot switch under the carpet).

Colossus · May 25, 2018

Very cool. You may want to post this over on the 1500 thread as well, or maybe a mod can make this a sticky. There will definitely be many interested in this.

silveradosid · May 25, 2018

great job i like this

paauto · May 25, 2018

On 5/24/2018 at 6:14 PM, paauto said:

I added an orange LED in my speedo cluster that lights up when I'm in 4WD. I tapped into the wires that feed the LED on the 2/4WD dial selector. The white wire in the factory harness is + and the brown/black wire is -. The BCM closes the ground circuit when in 4 Hi and allows the LED on the factory dial to illuminate. I simply piggybacked off of this. I have pictures of the whole installation and will post a link to them once I have my kid show me how to do it. I also have a blue LED on the opposite side to indicate when my light bar is on (I turn it on/off with a pneumatic foot switch under the carpet).

So here's a link to the step by step photos - www.paauto.weebly.com

Here's a rough overview of the install that corresponds to the pictures.

1. Collect the parts you need - LED light, 3M wire taps, 20 gauge wire, 24" or so of convoluted tubing to protect the new harness, soldering iron, heat shrink tubes, heat gun, wire stripper and compressed (canned) air.

2. Remove the the "visor" over the speedo. It is held in place by clips. You can start at one corner and lift with your fingers or you can use a trim removal tool and work your way around. I took a shot of the backside of the visor so you can see where the clips are.

3. Remove left fuse panel then remove the bezel that holds the Transfer Case and Headlight dials. Here again, all of this held by clips. Just pull the bezel straight out. Once out, release the three connectors and set the bezel/switch assembly aside.

4. Remove the two torx screws (T15) on the bottom of the knee panel on either side of the hood release lever. You want to be careful removing this piece. I forgot to take a pic of the backside of this piece - but there are two clips at the bottom of the piece. Pull them out one at a time. Once the bottom is free, push up on the edge of the bottom of the panel (pushing toward the steering wheel) to release the two top clips that are angled down. You may need to whack it with the palm of your hand to release the clips. You don't want to pull straight out on the top of the panel b/c the clips are angled down and will crack (I did it the first time and had to epoxy things back together). While not necessary, you can remove the hood release lever by pushing on the black clip and working the thing out. This allows you to set the knee panel aside so it's not dangling.

5. Now remove the 3 7mm bolts that hold the bezel in place. There are four clips that hold the bezel to the frame (see the picture of the back of the bezel). Start on one side and pull straight out on it and it will come free.

6. Remove the 4 7mm bolts that hold the speedo assembly in place. At this point I would remove the wire harness from the back of the speedo so you can take the assembly to your bench for the light install. Note that I did not do this b/c I already had an LED indicator light installed (for my light bar) and didn't want to disconnect that work. So, I had to do this install with the speedo still in the truck.

7. Take the speedo to your bench. Put down a clean, lint free towel. The clear lens is held on with several clips around the perimeter. Carefully work those clips off and remove the clear lens, setting it aside where it won't get dusty. Try not to touch the interior of the clear lens or the inside of the speedo b/c it may be difficult to get fingerprints off.

8. Drill a hole from the top (outside) of the speedo. You can see in my picture I drilled the hole in the second honeycomb from the right, in the back row. I did this slightly to the right of center of that honeycomb so not to block one of the indicators in the speedo itself, although I don't think that would have been an issue anyway. Obviously start with a small hole and through trial and error drill larger until the light fits in (from inside the speedo). If you are lucky, the light will self seat itself. I drilled the hole a bit too big for it to self seat so i put some epoxy on it on the outside to hold it in place.

9. Now, clean up the drill shavings from the speedo using some compressed air. Then replace the clear lens.

10. Cut yourself two 3 foot lengths of the 20 gauge wire and solder and end of each to the leads from the LED light you just installed. Slip some heat shrink tubing over wire to cover the solder and use the heat gun to shrink it. If you're using the same color wire, note which one is connected to the positive lead of the LED light. Next, cover the wires in the convoluted tubing and tape the end of the convoluted tubing with friction tape.

11. Take the speedo assembly back to the truck and feed the new harness down so it is hanging in the dash (see picture and note the harness to the left of the steering column). I also have a picture of where the new harness is fed from the top. Note that the factory speedo harness goes much further back into the dash through an opening. No need to follow that route.

12. Get a stiff wire, fish tape or coat hanger and pull the new harness to where the factory headlight and transfer case harnesses come out of the dash. Find the white connector. The white wire is +. Tap into this wire the positive lead from the LED light using a 3M wire tap. The Brown/Black wire is neutral (normally open) and is closed by the BCM when the transfer case is in 4WD, thereby completing the circuit. Tap into that wire the negative lead from the LED light. I used friction tape to tidy everything up as well as zip ties on the new harness in the dash.

12. Re-connect the connectors to the switches and replace the bezel and the fuse panel cover. Put the speedo back in with the clips and four bolts. Then the bezel. Then the knee pad - but put the top clips in first then the bottom ones then the torx screws. Lastly put the visor on and you should be good to go.

One small issue I noticed is the new LED glows faintly when the dusk sensor kicks in, turning on the background instrument lights. I will do some research and put a resistor on the positive lead and see if that fixes it.

gearheadesw · May 27, 2018

Wow, good job. How on earth do you guys figure this stuff out??

I must say that I enable the 4 wheel drive screen in the DIC whenever I shift into 4x4, but this is cool.

paauto · May 27, 2018

8 hours ago, gearheadesw said:

Wow, good job. How on earth do you guys figure this stuff out??

I must say that I enable the 4 wheel drive screen in the DIC whenever I shift into 4x4, but this is cool.

I'm a total weekend warrior. I laid my hands on the GMC Upfitter Integration Body Builder Manual for the truck. It is ~1200 pages long and has the full schematics, explanations of how things work, detail on every connecter in the truck, on and on and on. On page 92 it shows the schematics for the 4x4 transfer case indicator LEDs. I tried to post it on my weebly site, but it's too large to post without paying to upgrade.

paauto · July 1, 2018

I finally got around to adding a 10k ohm resistor to the positive feed for the new LED. Here was the issue. When the dusk sensor kicks in it sends 5 volts to the positive lead (the white lead) in the transfer case shift knob harness. Even if the knob is in 2HI, the ground circuit for the 4HI indicator closes and allows current to flow. I suppose this is to provide some backlighting in the factory knob. Anyway, this was dimly lighting up my new LED even if in 2HI at night.

The 10k ohm resistor reduces the current, significantly dimming the LED at night in 2HI. When in 4HI, all is good as the system sends 14 volts which allows the new LED to light brightly.

paauto · November 23, 2018

I did a bit more research and changed the wiring for the 4x4 indicator light so it is completely off even when the dusk sensor is on. I tapped into the Transfer Case Control Module - which is right above the gas pedal on the firewall. There are three connectors that plug into it. The top connector is the one you want. I pulled that connector out and wire tapped into the yellow/white stripped wire (see photo for exact wire) and connected that to the orange dash LED. I connected the ground from the orange LED to the body. I can report it works perfectly. When in 4x4, the LED is on and when in 2wd it is completely off (no more faint glow at night when the dusk sensor is on). No error codes.

The yellow/white wire that I tapped into is the feed for the factory 4x4 indicator in the DIC.