DIY Motorized Rear License Plate Mount - Instructions

Explore4x4AZ

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- - Long Post Disclaimer - - Skip to the video below if you just want to understand what a motorized license plate is

I’m not sure how many other people have a similar situation as me, but I have been a bit disappointed with the aftermarket options for license plate mounts. I know, this probably sounds a bit strange… but the aftermarket bumper my wife bought did not have a license plate mount, and the only options either had the plate hanging off the LH side of the vehicle (seemed easy to catch on brush), or mounted off-center in the spare tire (just looks a bit strange IMO). So being an engineer, and having a knack for overcomplicating things, I decided to make my own motorized license plate.

The concept is simple: mount the license plate in the center of the spare tire and use a servo to move it out of the way when you shift into reverse.



There is a bit more to it than that, but that's the gist.

I have had it on the jeep for 6+ months now, and it's still working strong. ALMOST the entire design is made of off the shelf or 3D printed materials, with the exception being the base bracket and the lug nuts adapter, which I got from a different license plate relocation kit. I had originally hoped to productionize the design and attempt to launch it as a product, but that's not in the cards at this time. So with that said, I figure I should share the design files with anyone else who may enjoy them! I'll also post a simple BOM with links at the end of the post.

The design is broken down into 5 main tasks:
  1. Signal / Communication
  2. Microcontroller / Breadboard
  3. Power
  4. Mounting
  5. Mechanism
I'll write a brief overview of each below. If there is enough interest, I'll come back and do a proper step-by-step DIY instruction.

1. Signal / Communication
The signal for this device comes from the driver's side tail lamp wire harness. More specifically (at least on the '18 JLU), pin 5 of this connector is the power to the reverse lamp, so we can use this as the signal for the system (This Forum post is an EXCELLENT source of info).​
Now I didn't want to just splice into this harness, since dealers love to void warranty over these types of things, so I went ahead and made my own bridging adapter using an inline 12 pin Molex MX-150 connector with a T split for pin 5. You can find these for ~ $3 / piece on websites like digikey, or even Amazon for that matter. All you need to do is remove the driver's side tail lamp (https://youtu.be/ORm-ZnbdCoQ ...skip to 1:11), disconnect the tail lamp from the vehicle side harness, connect your bridging adapter, and replace the tail lamp.​
1615177920381.png
Simple Diagram (green connectors is custom harness):​
1615178192175.png

You will now need to run your wires from the rear driver's side tail lamp into the storage area of the rear compartment, where the OEM spare tire jack is. I found the easiest way to do this was to run the wires under the rear of the vehicle and up through the drainage port at the bottom of this compartment. Within this compartment is where I have the microcontroller stored. From this point, you will need to run another wire harness from the microcontroller out to the spare tire (you don't NEED to talk the interior trim out as shown in the image below, it's just a bit cleaner install that way).​
1615179259095.png
1615181395843.png
At this point, all the connections should be made onto the breadboard housing the microcontroller (details in next section).​
2. Microcontroller / Breadboard

Originally I was using an Arduino Uno for this project, but it was pretty big and overpowered for what I was needing to do. To reduce cost and space, I down sized to an Arduino Nano. This is still far more capable than is needed, but it gets the job done for only about $3 / controller, which is very reasonable. Unfortunately, the only schematic I have is of the old Arduino Uno setup, so I'll post that below and if there is enough interest I'll create one for the Nano too:​
1615182158139.png
Something VERY important to note on this... the step down resistors from the custom bridge harness (circled in red). The vehicle runs on a 12V system. The maximum voltage input on the Arduino is usually around 5V, or less (for an analog input pin). After destroying two uno's I realized these resistors are rather important, so don't make my mistake! The final layout looks like this:​
1615180002551.png
I'll add an upload link for the Arduino code in the future, but it's pretty simple. The only tricky part about it is ensuring that the servo range matches the physical servo position, but more on that later.​
3. Power

Now this is where the instructions may deviate depending on what model you have. To make my life easy, I'm using the 12v cigarette lighter in the back storage compartment (I believe this is only on vehicles w/ the rear subwoofer). I simply bought a 12V plug (with a DC connection on the other end), and a 12V to 7.5V transformer. I chopped of the DC connection, spliced in the transformer to reduce the voltage to something Arduino will be happy with, and then added the necessary connectors to mate to the power connector in the image shown above. The last thing I had to do was switch the 12V outlet from always hot to ignition based (Tutorial here...Also in the manual).​
4. Mounting

This is the portion which is not so off-the-shelf. The one component I could not find easily, and which would be expensive to produce in low volumes, are the lug nut adapters for the spare tire. I happened to have these available from another project, so I used this and the base mounting bracket (shown in the below image as pink and purple, respectively).​

1615180731600.png
5. Mechanism

The mechanism itself is pretty straight forward. I'm using a 4-bar link with a single servo driving the system. In order to make the up/down actuation smooth (due to having only one servo), the bottom links are connected via a torsion bar. This torsion bar is snapped into the mounting bracket for quick access to the lug nuts if needed. The link arms are retained by external retaining rings to keep things cheap, light, and simple. All of the parts you see (minus the servo, hardware, base bracket, and lug nuts) are all 3D printed in ABS using a desktop FDM printer.​
The image below is the "Down" position. This is the default position which places the license plate in the center of the spare tire.​
1615180912605.png
1615181092051.png
And once shifted into reverse (or manually overridden via the switch), it will move to the "Up" position, shown below:​
1615181225258.png
1615181131325.png

The rest is pretty straightforward. I'll return to post the Bill of Materials, links to OTS components, and files for the 3D printed parts another night, and depending on interest, add more detailed instructions. Thank you guys for reading! - Kyle​
Images of it mounted:​
1615181738691.png
1615181776177.png





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tonygiotta

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So being an engineer, and having a knack for overcomplicating things, I decided to make my own motorized license plate.
I'd say that's a bit of an understatement... lol

But in all seriousness, I love the work/thought you put into this. Wish I had the knowledge to find the proper factory matched connectors such as what you used to make your T-harness. An added level of detail I'd love to work into some projects of my own.
 
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Explore4x4AZ

Explore4x4AZ

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lot of work just to back up.

just buy a couple L brackets and bolt it to the end of the bumper.
Fair point. That's what I started with. Just wanted the plate to be in the center of the tire.
 
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Explore4x4AZ

Explore4x4AZ

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I'd say that's a bit of an understatement... lol

But in all seriousness, I love the work/thought you put into this. Wish I had the knowledge to find the proper factory matched connectors such as what you used to make your T-harness. An added level of detail I'd love to work into some projects of my own.
I can send you a link to those connectors is you are interested. Yeah that T harness was a nice way to not mess with the factory harness.
 

TroyBoy

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Okay this is really cool. This reminds me of the tech kid on the Goonies. If I had the skills I would build it but just for the geek factor.
 

Volstock

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Very cool to see your process. I don't see any mention of a light to illuminate the plate. How are you meeting the legal requirements?
 
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Explore4x4AZ

Explore4x4AZ

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Very cool to see your process. I don't see any mention of a light to illuminate the plate. How are you meeting the legal requirements?
Good catch! That's on the todo list (so far no issues, knock on wood).

I was actually planning on reworking the bridge harness at the taillamps to also pick up the running lamp signal, then use that and the Arduino to power a license plate light (or just repurpose the old one down near the bumper).
 
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Explore4x4AZ

Explore4x4AZ

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Love it, but got to wonder if Rube Goldberg is your hero.
I'll admit, those machines are pretty cool!

My ultimate goal was to simplify this to be installable in under 30 minutes, with little to no wiring required. Still working on that idea though...
 
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Explore4x4AZ

Explore4x4AZ

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Okay this is really cool. This reminds me of the tech kid on the Goonies. If I had the skills I would build it but just for the geek factor.
When I get a little more time I'll post the files and links. The 3D printed parts you can order off of Shapeways or Xometry for relatively cheap.
 

Volstock

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Good catch! That's on the todo list (so far no issues, knock on wood).

I was actually planning on reworking the bridge harness at the taillamps to also pick up the running lamp signal, then use that and the Arduino to power a license plate light (or just repurpose the old one down near the bumper).
My only other comments would be:

- Why not pull power from the passenger side to minimize the wire length?
- Mount the Arduino in the tailgate for added protection from the elements.

After reading your post it sent me back looking at different bumpers I was considering and where/how I would relocate the license plate when I upgrade.

Curious to see how this progress as this version looks pretty damn cool.
 
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Explore4x4AZ

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My only other comments would be:

- Why not pull power from the passenger side to minimize the wire length?
- Mount the Arduino in the tailgate for added protection from the elements.

After reading your post it sent me back looking at different bumpers I was considering and where/how I would relocate the license plate when I upgrade.

Curious to see how this progress as this version looks pretty damn cool.
These are great ideas! I don't see any reason not to use the passenger taillight, and tailgate mount should work so long as it can package in without blocking the trim from going back on. 👍
 

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