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Discussion Starter · #1 ·
My first write up, so if theres a mistake in wording or description, my bad.

So if any of yall are like me and replaced your interior and cargo/bed lights with led bulbs, and realized that the interior leds are dim when switched on individually by the power buttons, but have full power when unlocked or a door is opened. Or that the rear cargo light will not fully power on until you switch on an incandescent light first and find it annoying and bothers you, then I have a fix for you. Took about 30 min with messing with the dog, taking pictures, and going slow. Plus meticulously taping and securing everything. Scroll a bit if you don't want to read the babble of my trying to explain the issue.

I cant take credit for figuring out the fix for this, but I do believe I am the first to try it on a 2500 and it work. I actually found a thread on another forum:
The dreaded "dim LED map light" fix is finally in progress. [Archive] - Cadillac forums : Cadillac Owners Forum

Now I cant guarantee that there will be no complications from this modification, but so far so good. Its only been a day, but I will update as time goes on.

Anyways, the reason why the leds are dim when switched on individually but fully bright when a door is opened or the truck is unlocked is because of our bcms. When you switch each bulb on individually the bulb is not drawing enough voltage to fully power on since these's led's are so efficient, and to get the bulb to fully power on, I would have to remove an led and replace it with a stock bulb. I found the 6 bulbs with the issue are the two front map lights, the two rear map lights, and the cargo lights. All have the issue because of the individual power switch to each bulb. I decided to go the resistor route and soldered resistors onto the rear festoon bulbs and that actually fixed the issue of the rear maps being dim. I tried the same with the front 194 bulbs but to no effect. I could get the bulbs to fully power on now by pressing one of the rear map light bulbs. This would also allow the cargo lamp to get full power. This got annoying.

So after hours of googling and tinkering, I found that there are 3 wires to each socket that has this issue. There is an orange wire, a black wire, and a gray wire with a black stripe.


The grey wire with the black stripe is the wire that supplies voltage to the lights when a door is unlocked or opened. This sends 12 volts and slowly fades off to produce the dimming effect.
The orange wire (EVIL WIRE) is our issue. This is the wire that leads from the bcm/brain to the bulbs. When the bcm is asleep it only sends a few volts to each bulb, we want a full 12v all the time.
Then you have your black ground.

So when we turn on our lights and they are dim, our bcm/brain is still asleep. That is why they will not turn fully on. When I got the brain to "wake up" you can hear an audible click and you have full power to the lights. So the plan is to remove the sleeping "brain" from the equation. To do this we have to cut the orange wire and reroute power to the bulbs from a good always 12v location. Reengineering gm.

Here are the supplies I used.
Microtorch
But Connectors
Add-A-Circuit -AutoZone-
Wire
Solder (optional)
Diodes -276-1653 from RadioShack-
Heat Shrink



First off you need to open your drivers door and find the cab fuse box.




Next look inside and find the wire loom that has a grey foam sleeve.




Go ahead and pull this wire loom away from the fuse box, it has a bunch of slack when pulled and allows room to work.



Then remove the black electrical tape from the loom and expose the wires.



Separate the orange wire from the rest of the loom. Now each trucks may be different so we are going to do some testing now.



Go ahead and grab a multimeter and test the wire. If you have a dim led issue, (whether interior or cargo lights) then when the light is switched on you should have around 5-6 volts. The cargo lights I think were 8 volts.



Once you get the lights to fully power you should have 12 volts now and a bright led.



Take the diode and either solder or but connect the diode in between the add-a-circuit and the extra wire you have. I planned on soldering, but tried a but connector first as a test and it secured well enough that I left it there. Make sure the diode has the grey line closer the wire you add, not the add-a-circuit. The diode only allows power to flow one way. If it is backwards then you will have no power.





Then add your heat shrink...



And shrink er down.



Next is the fun part. Cutting into your trucks wiring. Take the orange wire and cut it in half. Be absolutely positive that this wire is the wire we need. If in doubt, check continuity from this wire to the sockets to ensure you are correct.



Take your new circuit and but connect the orange wire to your added wire from the add-a-circuit or fuse tap. Then heat shrink the connections.



Plug in your add-a-circuit or fusetap and check the operation of the lights. You should have full power of the lights. I tapped into TBC 2A fuse. It controls the dashboard lights but is an always hot location at 15 amps.





Now that you have full power to the lights without any annoyances, you can tape up your old orange wire that leads to the bcm to prevent a short...



Tape up the full connection and reinsert the clip into the fuse box. Securing the circuit to prevent any looseness or noises.





Done! Put your cover back on the fuse box and shut the door. Crack open a cold beverage and enjoy your now never dim, bright leds. :drink


Disclaimer: By tapping into a always hot fuse location your lights will no longer time out. With the leds drawing no current your battery will probably take weeks to drain down. If you tap into a fuse that is only hot with the ignition on, your lights will only work by switch when the ignition is on. I am not a vehicle electrician but I am a fleet mechanic by trade. Soldering is a more permanent solution but I am not very good at it. If you run into issues don't be afraid to ask, and if you notice any issues with my post please advice me and I will change it. I want this to help anybody and everybody with a similar issue. Thanks for the read guys.:thumb
 

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Discussion Starter · #3 ·
Thanks man.
 

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I did this about a week ago. Probably spent about an hour total doing it, but that's also because I rewired one of my accessory feeds (I have front and back cameras fired from the ACC power fuse that are pigtailed together right before the "add a circuit")

The only issue I encountered was not knowing which side of the spliced harness was the feed side or the load side.

Took a bit of trial and error as I couldn't tell from the pictures supplied

Also I was ridiculously meticulous about documenting the before and after voltages and also the amperage draw on the new LEDs vs the stock incandescents.

Since I had replaced the cargo lights and CHMSL lights with LEDs, it wasn't that big of a deal to connect my clamp meter to measure DC amps either.



Sent from my SM-G935T using Tapatalk
 

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Discussion Starter · #5 ·
I did this about a week ago. Probably spent about an hour total doing it, but that's also because I rewired one of my accessory feeds (I have front and back cameras fired from the ACC power fuse that are pigtailed together right before the "add a circuit")

The only issue I encountered was not knowing which side of the spliced harness was the feed side or the load side.

Took a bit of trial and error as I couldn't tell from the pictures supplied

Also I was ridiculously meticulous about documenting the before and after voltages and also the amperage draw on the new LEDs vs the stock incandescents.

Since I had replaced the cargo lights and CHMSL lights with LEDs, it wasn't that big of a deal to connect my clamp meter to measure DC amps either.



Sent from my SM-G935T using Tapatalk
I'm glad its helped somebody. It's been 3 years this way and no issues.
 

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My first write up, so if theres a mistake in wording or description, my bad.

So if any of yall are like me and replaced your interior and cargo/bed lights with led bulbs, and realized that the interior leds are dim when switched on individually by the power buttons, but have full power when unlocked or a door is opened. Or that the rear cargo light will not fully power on until you switch on an incandescent light first and find it annoying and bothers you, then I have a fix for you. Took about 30 min with messing with the dog, taking pictures, and going slow. Plus meticulously taping and securing everything. Scroll a bit if you don't want to read the babble of my trying to explain the issue.

I cant take credit for figuring out the fix for this, but I do believe I am the first to try it on a 2500 and it work. I actually found a thread on another forum:
The dreaded "dim LED map light" fix is finally in progress. [Archive] - Cadillac forums : Cadillac Owners Forum

Now I cant guarantee that there will be no complications from this modification, but so far so good. Its only been a day, but I will update as time goes on.

Anyways, the reason why the leds are dim when switched on individually but fully bright when a door is opened or the truck is unlocked is because of our bcms. When you switch each bulb on individually the bulb is not drawing enough voltage to fully power on since these's led's are so efficient, and to get the bulb to fully power on, I would have to remove an led and replace it with a stock bulb. I found the 6 bulbs with the issue are the two front map lights, the two rear map lights, and the cargo lights. All have the issue because of the individual power switch to each bulb. I decided to go the resistor route and soldered resistors onto the rear festoon bulbs and that actually fixed the issue of the rear maps being dim. I tried the same with the front 194 bulbs but to no effect. I could get the bulbs to fully power on now by pressing one of the rear map light bulbs. This would also allow the cargo lamp to get full power. This got annoying.

So after hours of googling and tinkering, I found that there are 3 wires to each socket that has this issue. There is an orange wire, a black wire, and a gray wire with a black stripe.


The grey wire with the black stripe is the wire that supplies voltage to the lights when a door is unlocked or opened. This sends 12 volts and slowly fades off to produce the dimming effect.
The orange wire (EVIL WIRE) is our issue. This is the wire that leads from the bcm/brain to the bulbs. When the bcm is asleep it only sends a few volts to each bulb, we want a full 12v all the time.
Then you have your black ground.

So when we turn on our lights and they are dim, our bcm/brain is still asleep. That is why they will not turn fully on. When I got the brain to "wake up" you can hear an audible click and you have full power to the lights. So the plan is to remove the sleeping "brain" from the equation. To do this we have to cut the orange wire and reroute power to the bulbs from a good always 12v location. Reengineering gm.

Here are the supplies I used.
Microtorch
But Connectors
Add-A-Circuit -AutoZone-
Wire
Solder (optional)
Diodes -276-1653 from RadioShack-
Heat Shrink



First off you need to open your drivers door and find the cab fuse box.




Next look inside and find the wire loom that has a grey foam sleeve.




Go ahead and pull this wire loom away from the fuse box, it has a bunch of slack when pulled and allows room to work.



Then remove the black electrical tape from the loom and expose the wires.



Separate the orange wire from the rest of the loom. Now each trucks may be different so we are going to do some testing now.



Go ahead and grab a multimeter and test the wire. If you have a dim led issue, (whether interior or cargo lights) then when the light is switched on you should have around 5-6 volts. The cargo lights I think were 8 volts.



Once you get the lights to fully power you should have 12 volts now and a bright led.



Take the diode and either solder or but connect the diode in between the add-a-circuit and the extra wire you have. I planned on soldering, but tried a but connector first as a test and it secured well enough that I left it there. Make sure the diode has the grey line closer the wire you add, not the add-a-circuit. The diode only allows power to flow one way. If it is backwards then you will have no power.





Then add your heat shrink...



And shrink er down.



Next is the fun part. Cutting into your trucks wiring. Take the orange wire and cut it in half. Be absolutely positive that this wire is the wire we need. If in doubt, check continuity from this wire to the sockets to ensure you are correct.



Take your new circuit and but connect the orange wire to your added wire from the add-a-circuit or fuse tap. Then heat shrink the connections.



Plug in your add-a-circuit or fusetap and check the operation of the lights. You should have full power of the lights. I tapped into TBC 2A fuse. It controls the dashboard lights but is an always hot location at 15 amps.





Now that you have full power to the lights without any annoyances, you can tape up your old orange wire that leads to the bcm to prevent a short...



Tape up the full connection and reinsert the clip into the fuse box. Securing the circuit to prevent any looseness or noises.





Done! Put your cover back on the fuse box and shut the door. Crack open a cold beverage and enjoy your now never dim, bright leds. :drink


Disclaimer: By tapping into a always hot fuse location your lights will no longer time out. With the leds drawing no current your battery will probably take weeks to drain down. If you tap into a fuse that is only hot with the ignition on, your lights will only work by switch when the ignition is on. I am not a vehicle electrician but I am a fleet mechanic by trade. Soldering is a more permanent solution but I am not very good at it. If you run into issues don't be afraid to ask, and if you notice any issues with my post please advice me and I will change it. I want this to help anybody and everybody with a similar issue. Thanks for the read guys.:thumb
Which diode did you use that pack from radioshack has 4 different types?
 

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Discussion Starter · #7 ·
Which diode did you use that pack from radioshack has 4 different types?
Honestly, I don’t remember man. I think the pack that I had, had all the same diodes if I remember right.
 

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So question. Do you think wiring a resistor into that orange supply wire would fix the problem. I might be wrong but I've got to ask. Cause the bcm won't have a ground path for that circuit so it won't wake up till a light is powered on to give it one. But it will also give enough load to the bcm to tell it to give the circuit 12v. It seems like this is the same problem and solution as people having problems with hyperflashing blinkers.
 

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Yes, you could add a resistor into the circuit, but you defeat the whole idea of having low-current leds installed. Running led lamps is usually to cut your load so they can run for a much longer time. Also, that resistor will inherently get warm due to its job, basiclly adding resistance to the circuit by converting it to heat.

A common 1n5400 diode should be plenty for led lamps, as that is made for up to 3 amps of forward current. And if you have any other 1n54xx diode, those will work too, they just have higher voltage capability.
 
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