Adding LED Light Strips in Cargo Area - Let There Be Light! DIY How-To Writeup 💡

[dustang50]

Any word on the solid state relay? I recently wired in some LEDs and would love it if they shut off with the existing trunk light!

 

[GatorJ_MME]

I haven't tried this, but if you want to use a relay or similar approach, you need to know the voltage that the car is supplying on the switch signal (pin 2).

There are relays that can pass through 12V but only expect less than or equal to 5V on the control (switch) signal. If you have a multimeter, measure between pin 2 (positive) and pin 3 (negative), both when the trunk lights are on and off.

You just need to make sure you are selecting the right part based on the signals you are trying to leverage.

 

[Ghost Mach-E]

Wow! nice work. nice write up

 

[JohnFoxeSheets]

Any word on the solid state relay? I recently wired in some LEDs and would love it if they shut off with the existing trunk light!

I'm still testing, but I think it's going to work, though not quite in the way I initially envisioned. I'm waiting for another part to come in and hope to have it all finished this weekend. I'll do a write up when I am done.

 

[JohnFoxeSheets]

I finally finished my lighting. Here is a write up...

As you know, I decided to see if it is feasible to use the OEM lamp module to trigger a solid-state relay to turn on/off the added LED strips. (My initial idea actually was to try to use the third wire to C489 (Switch – Overhead Console # External Control) to trigger the relay, but I discovered that in fact that wire is the LIN bus to the module and so it cannot be used as a trigger. So I instead needed to do surgery on the OEM lamp module to extract a suitable trigger.

Before we go further, I want to stress that I do not recommend others do this mod! It is time consuming, could easily end up trashing your lamp module, and if things really go south it might even damage your BCM (which would be certifiably bad). If you decide to proceed, you’re on your own. I cannot be responsible for any issues that arise should you attempt this mod.

OK, enough of the backstory and warnings, here’s what I did.

To summarize, we have three input pins on C489 (the connector to the OEM lamp module):

1. Battery Saver +12V (this is on whenever the car is on and remains on for about 20 minutes after the car is shut off)
2. Switch – Overhead Console # External Control (LIN)
3. Ground

Courtesy @MyLittlePony2022

Pin 2 is the LIN bus and is not used (directly) for this project. Instead, we tap inside the lamp module to obtain the appropriate signal to use with our solid-state relay.

To open the module, you’ll need to remove the clear diffuser plastic by carefully prying it open from behind. There are small tabs that hold it in place and those tabs can be pushed out from behind. Once the diffuser is off, the lens assembly drops out (tapping the module onto its face helps), and then the PCB assembly can be gently pried out. It is simply press-fit in the module housing, so there’s little worry of damaging it if you’re careful.

Here is the disassembled module:

After much testing and basically trashing my lamp module, I determined that Test Point 5 (TP5) is the correct net (signal in a circuit) to drive the SS relay. Tapping that test point directly is not recommended because unless you can protect against all strain to the tap wire, there is a very high probability that you will damage the circuit and need to make repairs (like I did). And while it certainly isn’t for the faint of heart, the best way I could figure out to tap that net is to drill through the PCB. I used a 1/16” drill bit and carefully drilled at the spot shown in the photo below:

I then, on the other side of the PCB, scraped off a small section of the white coating in the area shown below:

This exposed bare copper which is on the same net as TP5 (and the “W” contact of D2, the yellow colored LED you see on the right side of the PCB shown above).

Below you can see my finished modification. You can run a small wire to the inner pad of the bare C1 spot if you’d like (it is part of the same net).

Do not tap only TP5. I initially did that, and the tap wire pulled up the test point and broke the signal trace. I needed to repair the trace and who knows how long it will last… (Luckily the lamp module isn’t too expensive.)

To switch the LED strips on and off I used a 12VDC Solid-State Relay with a 1-amp load rating (Omron G3SD-Z01P). I purchased it from Digikey.com but unfortunately, I purchased the last one they have in stock, so I don’t know if anyone (crazy enough to try this mod) can easily find it. If you do want to try the mod, I suggest you search for a 12VDC input solid state relay with at least a 1-amp load rating.

Here is the schematic of the very simple circuit used to drive the LED Strips:

And here is the wiring diagram that shows schematically how I chose to wire up the circuit:

Here is the finished wiring harness. I drilled a hole in the back of the housing for the trigger wire to pass through. You can see the wavey trigger wire coming out of the back and going to the relay. I added 3M locking tape (heavy duty Velcro) to the top of the relay to mount to the back of the housing, though I’d not mounted it yet in this photo.

Here’s everything all buttoned up:

I ran the two LED strips in series, with the wire connecting them running behind the soundproofing under the floor (below the lift gate sill trim). The trim is easy to remove: just two bolts on the inside easily visible, two bolts holding the tie-downs, and a few clips.

Here's the finished result:

Am I happy with the results? Yes! Would I do it again? No! Should you do it? You need to decide, but I really don't recommend it.

Oh, and here's what my trunk looked like an hour before the video was made:

 

[JohnFoxeSheets]

Any word on the solid state relay? I recently wired in some LEDs and would love it if they shut off with the existing trunk light!

See my last post on this thread.

 

[dustang50]

I had toyed with the idea of using a momentary switch (like the switch on a refrigerator door that turns the light on/off) but decided against it since we really don't need that much light too often. I think it would be possible & there appears to be several locations one can be placed but the wear-and-tear of it was the deciding factor for me. The push button switch is great! Thanks for the write-ups, everyone!