Adding A Dimming Dome Light To 2019 Chevrolet Tahoe

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nrod_tx

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As the title states, I’m trying to add a dimming dome light to my 2019 Chevy Tahoe. I paid an installer to do it, but he stated he wasn’t able to hook it up to where I open my doors it turns on. He wired it to the manual overhead switch, and the dome light also has manual switches for on and off. The installer stated the relay was making a fast clicking noise due to the dimming function of the light head.

while researching, I have found that a relay with a capacitor and a diode might fix the problem. But have no idea on how to wire it.



Dome light is a Whelen 6” dome light with negative trigger wires.



Currently wired to turn on by oem switch on vehicle overhead panel and light switch on dome light.



Attached picture diagram of dome light
 

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P71toZ71

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Edit: I talked to nrod_tx privately and he shared some more information, and linked me to his post on the12volt.com. His installer added some extension wires that don't all match the wire colors of the Whelen light. I've updated this post to better reflect the current situation.

It was making a fast clicking noise because he wired it wrong, based on what I see in the vehicle's electrical wiring diagrams. Hopefully the BCM wasn't damaged. That "OFF DOOR ON" switch only grounds one of two pins from the BCM, depending on the position it is in. It is not a negative "door open" signal. Here is the info on the wires that he tapped into:

Connector X316 Headliner Harness to Overhead Console Harness:
6GY/BUCourtesy Lamp Switch SignalCircuit 156
10YELED Backlight Dimming ControlCircuit 6817
17RD/YEBattery Positive VoltageCircuit 240

It looks like you have the Whelen 60CREGCS, from which I see:
Whelen WireExtension WirePresent UseStatus
RedRedConnected to "Battery Positive"Good
BlackBlackConnected to self-tapped groundGood enough
YellowWhiteConnected to "LED Backlight Dimming Control"Good
WhiteTealConnected to "Courtesy Lamp Switch Signal"Wrong

I don't see the yellow wire from the Whelen light anywhere, but you didn't mention it, so I'm not worried about it. Also, per the Whelen docs, that blue wire should be orange. Maybe they ran out of orange or made a change. *shrug*

Rather than tap into the five different door trigger wires near the BCM (and diode isolate them), it will probably be easier to tap into the positive signal for the existing lighting. This is especially true if you want the Whelen light to mimic the behavior of the other lights. The door trigger is only one of several different methods of activating the dome lights.

The first issue is that the Whelen door trigger wire is expecting a negative signal, but the "Courtesy Lamp Switch Signal" is positive. The polarity of that signal needs to be reversed. A standard relay can do that that as seen in the below image. Note that a flyback/snubber diode should be installed on the relay to protect the BCM.

pos2neg.gif

I haven't had the opportunity to verify (using a multimeter/oscilloscope), but I believe the "Courtesy Lamp Switch Signal" wire uses PWM (pulse width modulation) to control the factory dome lights. This is possibly going to be the second issue. Assuming the PWM signal ranges between 0 and ~12 Volts, you should be able to use a passive RC low pass filter to smooth out the pulses and provide a steady voltage to keep the relay from bouncing open and closed (contact chatter). Time for another image!

Passive_RC_Filter_featured.jpg
On the left, you have the "Courtesy Lamp Switch Signal," then an inline resistor. After that, you have a capacitor that is grounded, and the filtered signal that goes to the load. In this case, the load would be the relay in the previous image.

So, here's what I would do in your situation:
1. Prepare the relay by soldering a diode across pins 85 and 86. The end with the white band should be towards pin 86
2. Cut the teal wire, leaving enough to work with on each side of the cut
3. Attach the teal wire that comes from the vehicle wiring harness to pin 86 on the relay
4. Attach the teal wire that comes from the Whelen light to pin 87 on the relay
5. Connect pins 30 and 85 to ground (using another ring terminal at that self-tapping screw)

Test it out by opening the doors, using the key fob to lock/unlock the doors, etc. If it works, you're done. But, if it doesn't...
1. Disconnect the teal wire from pin 86
2. Connect the resistor between the teal wire and pin 86
3. Put the capacitor between pin 86 (long lead) and ground (short lead)

Keep in mind this will be in a vehicle that is subject to constant vibration. Make sure all connections are mechanically strong before you close everything up.
 
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Doubeleive

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Weird I didn't think about this, why is there a relay being used? does the whelen lamp require a relay? or is it dimmable without a relay?
if it does not require a relay then simply ground the whelen to the body and run the positive wire (with a fuse) to the bcm interior light output.
i added interior led's to my 18 in this manner and it works perfectly in junction with the factory interior lighting.
if you are not sure if the whelen is dimmable without a relay then connect it directly to a 9v battery if it lights up then it probably will work fine without a relay and will power up with the bcm output. just be sure to use the appropriate fuse the factory led's do not have much amp draw I would imagine the whelen has a bit more.
 

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