[CPS]

What it looks like with both sensor wires ran through the firewall:

 

[NavyCuda]

@darkgenerals… you have a scope! See if it’s the can bus!

runs

 

[Bods]

Well this really took off. I didn’t know there was an actual “dimmer” for the dashboard lighting on these. I tapped into that blue wire on the switches in the kick panel as my gauges “dim 30%” when the dash lights come on. I would presume that the “dimmer” only dims the instrument cluster backlighting and not the switches in that panel, but that’s just a guess…

 

[Bods]

Ah, ok I see now, I didn’t realise there was dimming controls next to the trip computer reset, well there you go oops…. I’ll have a look into it a bit more in that case

 

[Bods]

Ok, here is the pinout of the factory illumination switch

i don't know why it's sideways, but it isn't going to let me fix it either

I'll attach the picture of how it interfaces with the gauge cluster, but looking at it, I assume it is only to dim gauges, there is a single wire to the BCM, which is a ground wire.

Illumination control would be the dimming function, but it's simply a NO/NC switch setup.

 

[Bods]

 

[Bods]

 

[Bods]

So it would appear that's only for the cluster backlighting, so won't be any good for a reference. As I mentioned above, I simply tapped into the blue wire on mine to get a 12v signal to dim the gauges I've got fitted. I'm not sure how low you wanted yours to go, but I've fitted resistors to autometer LED backlit gauges I used in a previous vehicle as they were way too bright at night.

 

[CPS]

So it would appear that's only for the cluster backlighting, so won't be any good for a reference. As I mentioned above, I simply tapped into the blue wire on mine to get a 12v signal to dim the gauges I've got fitted. I'm not sure how low you wanted yours to go, but I've fitted resistors to autometer LED backlit gauges I used in a previous vehicle as they were way too bright at night.

Thank you for the information! I was just looking for a wire that would drop in voltage (checking with multimeter) as the “-“ button was pressed. So just to clarify, by tapping into the “blue” wire you are just getting a switched 12 volt power source only when the headlights are turned on, but your gauges do NOT dim? Is that correct

 

[Bods]

Thank you for the information! I was just looking for a wire that would drop in voltage (checking with multimeter) as the “-“ button was pressed. So just to clarify, by tapping into the “blue” wire you are just getting a switched 12 volt power source only when the headlights are turned on, but your gauges do NOT dim? Is that correct

My gauges do dim, but the glow shift ones are built with a dimming wire that is referenced off a 12v supply.

So, more directly, no, they don’t dim the same as the instrument panel, they dim because they’re built that way. Other brand gauges may differ, some may not dim at all.

 

[CPS]

My gauges do dim, but the glow shift ones are built with a dimming wire that is referenced off a 12v supply.

So, more directly, no, they don’t dim the same as the instrument panel, they dim because they’re built that way. Other brand gauges may differ, some may not dim at all.

OK, thank you, that’s what I needed to know. So basically the blue switched wire for our truck is going to be a constant 12 V power source when the headlight switch is turned on. Im thinking our trucks use multiple wires to dim all the switches and gauge clusters (both blue and grey wires) like a CANBUS system.
My last option:
There is a small map light on the center overhead console (next to the back rear window opener switch) that DOES dim when the dimmer switch is pressed “+” or “-“. I do know for a fact it has a two wires setup. Hopefully tonight after work and when it gets dark, I will use my multimeter and spec out those 2 wires and see if the voltage drops from 12 volts when I turn the dimmer switch all the way down. If this works, I can trace this wire down one of the A-pillars and tap into this wire for the dimming wire.
If not, I give in and will use the 12 volt blue wire on the back of the dimmer switch and see what happens. I’m ready to put my trucks interior back together and move on to the sensors.

 

[CPS]

This map light:

 

[CPS]

Back of the map light:

 

[NavyCuda]

Where is the best pass through location anyways? I had a look on the passenger side as I want to pass through the J1939 backbone. I didn't see any decent real estate to punch a hole into. I haven't looked closer at the left side though.

 

[CPS]

Where is the best pass through location anyways? I had a look on the passenger side as I want to pass through the J1939 backbone. I didn't see any decent real estate to punch a hole into. I haven't looked closer at the left side though.

Are you talking about the firewall on the driver side? I posted the firewall pass through in Post 58-Post 61.

 

[NavyCuda]

Are you talking about the firewall on the driver side? I posted the firewall pass through in Post 58-Post 61.

Yeah I saw that picture and then asked my question... my brain must be mush right now.

 

[CPS]

Yeah I saw that picture and then asked my question... my brain must be mush right now.

lol…..no worries! Thats how I feel chasing down this darn dimmer wire. It’s holding me up from installing the 2 sensors! Hehe

 

[CPS]

Where is the best pass through location anyways? I had a look on the passenger side as I want to pass through the J1939 backbone. I didn't see any decent real estate to punch a hole into. I haven't looked closer at the left side though.

You have to cut and remove the carpet padding to get to it, and the removal of the module next to it will make it a whole lot easier. Both of my wires fit perfectly once I trimmed the center section of the rubber grommet out and re-installed it:

 

[CPS]

I finished my wiring harness. Unfortunately the map light didn’t work out either, so I did in fact tap into the “blue wire” on the dimmer switch plug (see previous pictures). Our trucks do use multiple wires for illumination so I can confirm this blue wire does NOT dim the gauges when the “+” and “-“ buttons are pressed on the dimmer switch. The good thing is that my ISSPRO gauges back lighting at a full 12V is about half as bright as the Titan XD gauges are at full brightness so the dimmer feature won’t be a problem. The blue wire on the dimmer switch is used as a full 12V current to “turn on” the back lighting on the aftermarket gauges when the headlight switch is turned to on or AUTO. I also used these quick connect T-Taps from Amazon to tap into the blue wire on the dimmer switch. I also put electrical tape around the T-Taps. These T-Taps are awesome, I wish I would have found them sooner. The rest of the wiring harness for the gauges I made from scratch.

 

[CPS]

T-Tap installed on blue wire and the orange wire branches off to both gauges dimmer wire.