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Discussion Starter · #1 ·
I'm working on a little lighting project, which I will detail more fully when I finish. For the moment I would appreciate a second opinion on the wiring, check my logic so to speak.

I will be using LED's.

I'm planning on using SPDT switches. (ON-OFF-ON)

This is a switched ground system. The center pin goes to the (-) side of the LED's, the selected switch position pins pick which ground I want to use. The 2 grounds I will be using are the cargo light BCM wire, and the rear door switch. (Which is a switched ground itself.)

Always on 12v will be tapped off rear 12v plug. (Amp draw will be miniscule, less than 1A total, and I will fuse it at that.) But, what I do not like is it is always hot. But I need it that way to accommodate a function.

Desired operation:

On position: Uses door switch, continuous on (no timeout.) Will illuminate with door opening, and will shut off when the door is closed. (To avoid accidentally leaving it on and getting in to leave and finding the interior lit up.)

Off position: Off, no matter what.

Auto position: Mimics OEM cargo light, times out using BCM. (This should not interfere with the OEM light.)​

What I am having a concern with is the door switch, or rather interaction with the BCM in general. I'd prefer to completely isolate an accessory circuit, but if I do that I will not be able to take advantage of BCM controlled switching which is what I want.

The BCM knows when that door is opened as it is a switched ground itself, so my belief is that the wire I want to tap is "Hot +" side, and my LED circuit should be isolated from ground, but the line where I need to tap goes back to the BCM, and who knows what it does in different situations. For all I know 20 minutes into my drive it switches to grounded and pop my lights will come on, or worse an always on 12v connection to the BCM may have undesired side effects.

I have marked my intended splice points on the wiring diagrams below. It makes sense if it is a simple grounded/ not grounded situation, but those diagrams only cover the interior lighting aspect of the wiring.



 

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Electrically your idea looks OK, I have only one concern...

The BCM monitors the power drawn from the BCM on pin 49 and 63 and, after a certain threshold (time or current drawn ?), it removes the ground to protect the battery.

I'm not sure if the LED's will draw enough current to trigger the protection system... so when your switch is in the 'always on' mode, it might stays on as long as the battery can hold it...

Some of us have replaced the cargo and other indoor light by LED's maybe they can tell us if the auto shutdown is still working.

This is just my opinion, don't take it as truth.
 

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Discussion Starter · #4 ·
Thanks for the input guys.

I have LED units in all the stock fixtures, they work fine.

I think what I may end up doing is setting this stuff up uninstalled with jumper wires and experimenting. I have easy access to the wires.

I may address my issue with having a 12v always hot connection to the BCM, by using a diode (marked with circle) to keep my spliced wire from powering that line when the BCM is off. All it does is sense when the door is open because it becomes grounded, the diode will allow power to flow to ground, but restrict my hot wire from back feeding it when it is not receiving 12v from the BCM.

 
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